Tracking Devices: How do they bleepin' work?
April 25, 2011 10:48 AM Subscribe
Follow-up: What could temporarily block or disable the tracking anklet my fictional character is wearing?
I posted a related question a few months ago, and the responses were enormously helpful, so here I am with some follow-up:
First of all, I just realized that I don't even know how tracking anklets are generally locked and unlocked. Is it by a key? The computer system they're connected to? If it were unlocked with the actual key, would it bypass the whole alert system?
Secondly, is there any sort of outside influence that could surreptitiously interfere with or disrupt the transmission from the anklet? I'm thinking that I want my protagonist to be abducted at some point, but if there's somebody out there who knows exactly where he is, it makes for a much less dramatic rescue and/or escape. I'm wondering if there's a way communication could be cut off so that he actually regrets the fact that it's not working for once...
Ideas? Any input you all have would be awesome and highly appreciated.
I posted a related question a few months ago, and the responses were enormously helpful, so here I am with some follow-up:
First of all, I just realized that I don't even know how tracking anklets are generally locked and unlocked. Is it by a key? The computer system they're connected to? If it were unlocked with the actual key, would it bypass the whole alert system?
Secondly, is there any sort of outside influence that could surreptitiously interfere with or disrupt the transmission from the anklet? I'm thinking that I want my protagonist to be abducted at some point, but if there's somebody out there who knows exactly where he is, it makes for a much less dramatic rescue and/or escape. I'm wondering if there's a way communication could be cut off so that he actually regrets the fact that it's not working for once...
Ideas? Any input you all have would be awesome and highly appreciated.
a wire mesh Faraday cage will block the ability of the anklet to transmit location data... but would these kidnappers not just cut the tracking device off their victim? what reason would they have to leave it attached but disabled?
posted by russm at 11:04 AM on April 25, 2011
posted by russm at 11:04 AM on April 25, 2011
Response by poster: Would this Faraday Cage prevent the alert from going off? Or would the system be alerted the minute the device stopped responding? Because cutting the device would do that in my guy's case.
posted by baronessa at 11:11 AM on April 25, 2011
posted by baronessa at 11:11 AM on April 25, 2011
At timed intervals, the ankle monitor sends a radio frequency signal containing location and other information to a receiver. If an offender moves outside of an allowed range, the police will be notified.
So the police don't necessarily know where they are, just that they are not where they should be.
posted by Lanark at 11:13 AM on April 25, 2011
So the police don't necessarily know where they are, just that they are not where they should be.
posted by Lanark at 11:13 AM on April 25, 2011
Response by poster: In my story, the "offender" has to stay within a 1 mile radius or he'll trip the alarm. I was sort of under the impression that this needed to be done via GPS, but is that wrong? Can that work with the radio signal? Also, does anybody know how these lock?
posted by baronessa at 11:19 AM on April 25, 2011
posted by baronessa at 11:19 AM on April 25, 2011
If the intended purpose of the monitoring device is to make sure that someone stays put, then there's not much that a kidnapper could do that a person that wanted to escape also couldn't do, other than perhaps saw off the limb. In other words, sure, you can hit it with a hammer, cut it off, or block its signal with shielding, but it's designed to detect those actions and notify the authorities if you try those things, otherwise it wouldn't be very useful. So really what you're talking about here is what the timeframe is, not whether the authorities would notice. If the kidnappers have a van ready and grab they guy and immediately disable the device, then it may not matter that an alarm would be going off at the authorities within 15 minutes or whatever because they'd already be speeding off on the interstate.
The only other attack would be to get someone on the inside of the monitoring company to disable it in the intended manner, but that opens a whole other bunch of complications because eventually someone's going to find out, so you're just back to talking about timeframes again.
posted by Rhomboid at 11:32 AM on April 25, 2011
The only other attack would be to get someone on the inside of the monitoring company to disable it in the intended manner, but that opens a whole other bunch of complications because eventually someone's going to find out, so you're just back to talking about timeframes again.
posted by Rhomboid at 11:32 AM on April 25, 2011
In the UK ankle tracking devices are almost uniformly monitored by private companies who (in my experience) are happy to hire people who are dodgy as all fuck. With that being the case it's not uncommon for the trackee to provide the tracker with drugs/sex/money to have a "technical problem" with the ankle bracelet that allows the trackee to get out and about at will for a 24hr period.
The hardware/software and the ankle bracelets themselves are all designed by the lowest bidder and malfunction so often that one of the fellows I know who worked for a tracking company had a side job as a taxi driver so he could earn money whilst driving from place to place to fix/replace the hardware. He was also perfectly happy to ignore infractions so long as the reason met his extremely low standard and/or weed was provided (see above).
So far as the locking mechanism on the ankle bracelet, those which I have seen (again UK-centric) come with either stretching lycra-esque bands or a thicker version of the sort of thing you'd find on an adjustable baseball cap as some of the folks who must wear the trackers are not exactly the slimfast set.
Here's a link to some pics of harder-to-abuse criminal GPS tracking kit. You can see the lock mechanisms on some of these as well as some technical data as to how they work (i.e. cellular GPRS or via SMS, update regularity etc).
On preview - Rhomboid also notes this factor - the weakest point in any security system is human. You can have laser retina scanners, voiceprint analysis or whatever but if you let the guy behind you in through the door then it's all for naught. Social engineering is the best way to exploit a real-world security system.
posted by longbaugh at 11:46 AM on April 25, 2011 [2 favorites]
The hardware/software and the ankle bracelets themselves are all designed by the lowest bidder and malfunction so often that one of the fellows I know who worked for a tracking company had a side job as a taxi driver so he could earn money whilst driving from place to place to fix/replace the hardware. He was also perfectly happy to ignore infractions so long as the reason met his extremely low standard and/or weed was provided (see above).
So far as the locking mechanism on the ankle bracelet, those which I have seen (again UK-centric) come with either stretching lycra-esque bands or a thicker version of the sort of thing you'd find on an adjustable baseball cap as some of the folks who must wear the trackers are not exactly the slimfast set.
Here's a link to some pics of harder-to-abuse criminal GPS tracking kit. You can see the lock mechanisms on some of these as well as some technical data as to how they work (i.e. cellular GPRS or via SMS, update regularity etc).
On preview - Rhomboid also notes this factor - the weakest point in any security system is human. You can have laser retina scanners, voiceprint analysis or whatever but if you let the guy behind you in through the door then it's all for naught. Social engineering is the best way to exploit a real-world security system.
posted by longbaugh at 11:46 AM on April 25, 2011 [2 favorites]
Here is another example of a tracking bracelet - it's just a simple belt/watch style attachment in this instance. From a general Google image search there isn't anything physically difficult about removing any of these devices. I've seen one where the locking mechanism is inside the main unit section (so it cannot be accessed without disturbing the mechanism's housing). It seems to connect together in a similar fashion to a seat-belt but can only be unlocked with a key without disturbing the tamper alarm.
A couple of minutes with a hacksaw is easily sufficient to remove even the best of these devices. There is literally no way that any local law enforcement team would be able to respond in time to catch anyone at it and if you knew it was updating hourly and when you could be miles away before anyone caught a whiff that you'd done a runner.
So far as anything else affecting the signal - think about your mobile/cellular phone - do you get good signal in some places and bad in others? It's much the same sort of thing. I'll defer to people with a decent understanding of signal propogation here - I know next to bugger all about that side of things.
posted by longbaugh at 12:07 PM on April 25, 2011
A couple of minutes with a hacksaw is easily sufficient to remove even the best of these devices. There is literally no way that any local law enforcement team would be able to respond in time to catch anyone at it and if you knew it was updating hourly and when you could be miles away before anyone caught a whiff that you'd done a runner.
So far as anything else affecting the signal - think about your mobile/cellular phone - do you get good signal in some places and bad in others? It's much the same sort of thing. I'll defer to people with a decent understanding of signal propogation here - I know next to bugger all about that side of things.
posted by longbaugh at 12:07 PM on April 25, 2011
I think it would be cool if the system just doesn't work because no-one really cares about enforcing it. The bracelet eventually sends its signal, a notification eventually appears on a guys screen, and he just flicks back to playing minesweeper. No need to do the paperwork unless you have to - no doubt the guy will be back soon enough. Meanwhile, the bracelet wearer thinks that the bracelet will be his savior and fully expects screaming sirens any minute now...
I don't know how the monitoring is done though, I just wanted to say that an unexpectedly low tech, human reason for a high tech bracelet not working, seems better to me.
posted by -harlequin- at 12:48 PM on April 25, 2011
I don't know how the monitoring is done though, I just wanted to say that an unexpectedly low tech, human reason for a high tech bracelet not working, seems better to me.
posted by -harlequin- at 12:48 PM on April 25, 2011
It might be tough to show how an abductor could know a) how often the device transmits b) how long it would take for the monitoring agency to realize there was a problem and alert law enforcement and c) how long it would take them to respond once alerted. But, there's probably a good sized margin of error for some of them so it's not unimaginable that the monitoring agency won't immediately alert law enforcement until a second or third transmission is missed. So simply cutting off the device, leaving it in the house and taking the subject to another location could easily work especially if the subject wasn't considered particularly dangerous to begin with. Law enforcement would eventually discover the subject is no longer wearing the device, but that would be about it.
posted by tommasz at 12:55 PM on April 25, 2011
posted by tommasz at 12:55 PM on April 25, 2011
My mom used to be a deputized probation officer and don and doff them from prisoners.
Yeah, without going into detail, there are essentially two types of ankle bracelets out there. The passive type requires the offender to be near a phone at check-in times. The bracelet has a receiver that is plugged into the phone line and at 4:00 pm, say, will try to "ping" the bracelet. If it's out of range, and think the effective range of a portable phone handset here, the device calls in a negative and notification goes back to the local constabulary.
The active type uses GPS and basically a small cellular transmitter that constantly sends its position back to a base.
We have a fairly innovative county sheriff with a big monitoring program for non-violent and other eligible offenders. At the same time they have to monitor released sex offenders under state probation. He's said that they can be as detailed as they want with these bracelets. For instance, the GPS could have areas around schools and bars blocked off, and if they get within these circles, the device sounds an alarm back at base. People out on bond can be prevented from getting near the home of a victim in their case. Or they can just be on house arrest but be allowed travel to and from a workplace along a defined corridor. It's basically a matter of painting with a mouse on a map. (This is all handled by a contractor, but under the sheriff's direction.)
All that said, the best way to defeat this is probably social engineering -- bribery of a probation official or the contractor, or hacking into the alarm system, if your story allows for those tangents. I'm not sure that technically defeating it is something that would be appropriate outside of an Enemy of the State style scenario. Possibly a technical flaw in the device could be exploited.
The simplest would be just them greasing it up and slipping it off of their unusually flexible ankle -- women particularly have been known to accomplish this. Like being able to pull your legs through your arms when handcuffed behind your back.
But they're designed to resist brute force approaches like being cut off.
posted by dhartung at 1:03 PM on April 25, 2011
Yeah, without going into detail, there are essentially two types of ankle bracelets out there. The passive type requires the offender to be near a phone at check-in times. The bracelet has a receiver that is plugged into the phone line and at 4:00 pm, say, will try to "ping" the bracelet. If it's out of range, and think the effective range of a portable phone handset here, the device calls in a negative and notification goes back to the local constabulary.
The active type uses GPS and basically a small cellular transmitter that constantly sends its position back to a base.
We have a fairly innovative county sheriff with a big monitoring program for non-violent and other eligible offenders. At the same time they have to monitor released sex offenders under state probation. He's said that they can be as detailed as they want with these bracelets. For instance, the GPS could have areas around schools and bars blocked off, and if they get within these circles, the device sounds an alarm back at base. People out on bond can be prevented from getting near the home of a victim in their case. Or they can just be on house arrest but be allowed travel to and from a workplace along a defined corridor. It's basically a matter of painting with a mouse on a map. (This is all handled by a contractor, but under the sheriff's direction.)
All that said, the best way to defeat this is probably social engineering -- bribery of a probation official or the contractor, or hacking into the alarm system, if your story allows for those tangents. I'm not sure that technically defeating it is something that would be appropriate outside of an Enemy of the State style scenario. Possibly a technical flaw in the device could be exploited.
The simplest would be just them greasing it up and slipping it off of their unusually flexible ankle -- women particularly have been known to accomplish this. Like being able to pull your legs through your arms when handcuffed behind your back.
But they're designed to resist brute force approaches like being cut off.
posted by dhartung at 1:03 PM on April 25, 2011
There was an article that made its way around the web about GPS jammers last month.
posted by exhilaration at 2:28 PM on April 25, 2011
posted by exhilaration at 2:28 PM on April 25, 2011
Maybe you could have your character lose a lot of weight, and then discover he can get out of the anklet as a benefit of getting fit, and take advantage of this a few times by sneaking out to the local pool hall or something.
Then, while he has the anklet off, he is actually abducted and is kicking himself for ever slipping out of it. And your readers figure he is in trouble, because they know he has done this.
But then he is found in some other manner he had not anticipated, like the location services or GPS from his iPhone or Android.
posted by misha at 2:45 PM on April 25, 2011
Then, while he has the anklet off, he is actually abducted and is kicking himself for ever slipping out of it. And your readers figure he is in trouble, because they know he has done this.
But then he is found in some other manner he had not anticipated, like the location services or GPS from his iPhone or Android.
posted by misha at 2:45 PM on April 25, 2011
Maybe you could have your character lose a lot of weight, and then discover he can get out of the anklet as a benefit of getting fit
Unless the character was really, really fat the limiting factor will be the ankle bone, not fleshy matter. Losing weight isn't going to make your ankle bone smaller.
posted by Justinian at 5:13 PM on April 25, 2011
Unless the character was really, really fat the limiting factor will be the ankle bone, not fleshy matter. Losing weight isn't going to make your ankle bone smaller.
posted by Justinian at 5:13 PM on April 25, 2011
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If the baddies are tech-savvy and are aware of his anklet they could have engineered a small Faraday cage to snap around it, blocking all transmissions.
posted by kindall at 11:01 AM on April 25, 2011