Please help me put together a remote office door unlock system for a local non profit.
September 30, 2009 9:37 AM   Subscribe

At secure offices, you have to get buzzed in the door. Help me build one of those systems for a local non-profit. Bonus points for inexpensive and practical for home use too!

First off, I can't even really figure out what to google. I've tried "security door controls" and I get some good looking stuff, but I don't know the right terminology for what I'm looking for. So here goes.

I want a button under or at a desk (or multiple desks) that, when pressed, unlocks a door on the floor below. This is NOT a high security application, it does NOT need to be bulletproof. There are some ladies who work alone at this rural agency in the mornings, and they'd like to let people in the building w/o letting them in the office, but there's a stairwell...etc.

Ideally we can do this on the cheeeep, something homebrew would be totally fine. Very little money to work with here, everything goes to youth programming, and we'd like it to stay that way. T'would also be a fun project for our new me.

It doesn't *have* to be a door-bell like button, it could be a keyfob, but we're thinking low-voltage wires are the way to go.

There are three desks who would like to have access to the button, so I'm guessing three buttons!

You tell me!
posted by TomMelee to Work & Money (12 answers total) 2 users marked this as a favorite
A google search for "homebrew door buzzing system" lead me to this high level diagram of such a system which identifies the major components that you are going to need. In particular you are going to need an electric strike to physically control whether the door can be opened or not.
posted by mmascolino at 9:55 AM on September 30, 2009

How about one of these?
posted by gregr at 9:58 AM on September 30, 2009

Ideally we can do this on the cheeeep, something homebrew would be totally fine.

Here's an Instructables article about how to make a DIY remote door lock system with around $30 in parts. I'm not sure if the exact hardware they are talking about will work for you, but the basic idea (wireless RF remote + electric lock) seems like it would suit your needs.
posted by burnmp3s at 9:59 AM on September 30, 2009

You're looking for "access control." Try
posted by torquemaniac at 10:14 AM on September 30, 2009

The advice above is good but I wanted to point out that there are a few very good reasons why systems like this are expensive. You need to think hard about the failure modes (electrical failure, mechanical failure, human error, etc) for whatever you build since the consequences can be bad.

Your best case failure: People can't get inside for work that day, or can't lock the door at night. Bad failure: Exit from a burning building is compromised.

Most systems like this will have a crash bar on the inside so you can always get out even if the solenoid/etc. is stuck. It's worth thinking through some of these situations since (again, best case) you run the risk of getting the organization in trouble with the fire inspector for using DIY door locks.
posted by range at 10:42 AM on September 30, 2009

Thanks for the inputs so far folks. I already knew about X-10 and was kind of trying to avoid it. I guess I forgot to leave that part out.

The other articles definitely help point me in the right direction.

The nice thing about this particular application is that they have a MASSIVE firedoor on their level that leads directly outside. Failure means they use another door. Of course, I'm seeing 12v and 9v stepdowns, so I could just wire in a battery after the transformer, couldn't I?
posted by TomMelee at 10:57 AM on September 30, 2009

You'd likely need a relatively large battery to supply the current needed for an electric strike. But that doesn't matter anyway. The door will still be normally operable by the handle and with a key from the outside.
posted by 6550 at 11:18 AM on September 30, 2009

whatever system you build should have a manual override so that the door can be opened from the inside...

Fire + door unable to be opened = bad news, even if there are other exits. People will tend to go towards the door they use the most in an emergency, if the building is filled with smoke and a bunch of other people rushing to get out the same locked door it would not be pretty.

Also, I doubt they will pass their fire inspection with an egress door that does not have panic hardware (or any hardware!) on it. At least in my area the fire captains go to each business at least once a year to look for violations.
posted by outsider at 11:33 AM on September 30, 2009

No idea if this is something that is in the DIY realm or not, but a place I worked at had a security system that consisted of a large electromagnet that held the door shut (door had a metal plate welded to it).

At night the door was just locked in the normal fashion, during the day the magnet held it shut and the power was controlled by the person on the reception desk. It always seemed to be a fairly simple security method to me and (presumably) if there was a power failure during the daytime hours, the door was automatically unlocked.
posted by 543DoublePlay at 12:58 PM on September 30, 2009

"Failure means they use another door"

You just want to make sure you get a Fail-safe magnetic strike system rather than a Fail-secure one. (In case of power/system failure, fail into the "open" position, not "closed"). So at night you would still want to deadbolt this door, so a burglar couldn't just cut the power, for example.
posted by misterbrandt at 1:02 PM on September 30, 2009

Misterbrant has it: make sure when the battery or power dies, the door sticks open, not locked. Heck, the other way might even be a fire-code violation.

Which means you must not think of this as the 'real' lock: that should be a regular old fashioned key-based one. This is just the "while we're open" convenience.
posted by rokusan at 2:23 AM on October 1, 2009

Rokusan--exactly. I guess I failed to say that part. This isn't the "real" lock by any means, that's why I said it's NOT high security. Fail-open was the plan too, I'm aware of the 2-exits rule.

This is simply a "while the ladies are up there alone in a big building in the middle of nowhere" security feature.

I've also been thinking the crash-bar angle is nice too, going out doesn't require that you be let out...but getting in means being let in.
posted by TomMelee at 7:17 AM on October 1, 2009

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