Steam Detector?

May 7, 2009 9:00 AM

Why does my smoke detector go off after I take a shower?

This only seems to happen in mornings when I'm home by myself, it's never happened when my husband is around. About 10 minutes after getting out of the shower, one of our smoke detectors goes off. It is in the room at the opposite end of the hallway from the bathroom (maybe 12 feet away). There is a smoke detector in the hallway directly outside the bathroom which has never gone off. The only way to get it to stop is to remove the battery for a while. It doesn't happen every day, or even once a week or once a month, but often enough that I've noticed the pattern.

The first time this happened, when I didn't find anything on fire, I thought the batteries needed to be changed. That didn't solve the problem. I was thinking the steam when I open the bathroom door might cause it, but 1) doesn't a smoke detector know the difference between smoke and steam? and 2) why wouldn't that set off the detector directly outside the bathroom door? and 3) why does it only seem to happen when I'm alone?

posted by LolaGeek to home & garden (11 comments total)

Check that the sensor is clean. A dirty sensor can cause a false alarm. Perhaps water vapor is adhering to the dust on the sensor.

As to why it only happens when you are alone... who knows. Maybe you open the bathroom door sooner than when your husband is around, allowing more water vapor to escape.
posted by The Deej at 9:03 AM on May 7

How old is the smoke detector. They do wear out and become more sensitive.

A smoke detector works by sensing the number of alpha particles emitted by a piece of Americum. Smoke stops the alpha particles. As the detector gets old the 'half life' of the Americum causes fewer Alpha particles to be emitted. Perhaps the steam/condensation is enoughto stop the already borderline number of Alpha particles reaching the sensor.
posted by Confess, Fletch at 9:11 AM on May 7

Older smoke detectors were set off by steam. Get a newer detector.
posted by JJ86 at 9:13 AM on May 7 [1 favorite]

the smoke alarm in our house goes off on hot humid days. so ya, humidity can affect them. maybe the newer models are less prone to that.
posted by jak68 at 9:43 AM on May 7

Turn on the bathroom vent while you shower.
posted by JuiceBoxHero at 11:22 AM on May 7

As the detector gets old the 'half life' of the Americum causes fewer Alpha particles to be emitted. Perhaps the steam/condensation is enoughto stop the already borderline number of Alpha particles reaching the sensor.

This is probably wrong - smoke detectors contain Am-241, with a half life of 433 years, to avoid this exact situation.
posted by Dr Dracator at 11:25 AM on May 7

Confess, Fletch: The isotope if Americium used in a smoke detector has a half-life of 432 years. That means after the 50 years since the smoke detector was invented, you'd still have 92% of your original Americium.

However in looking around I found this: "In either type of detector, steam or high humidity can lead to condensation on the circuit board and sensor, causing the alarm to sound".

This is almost certainly what's happening in your case. I don't think there's any super-easy way to avoid this. Improving your bathroom ventilation would help, and probably so would spending a little bit more time toweling off before you open the bathroom door.

If the smoke detector outside your bathroom door is warmer than the one at the end of the hall it will attract less condensation. I guess maybe warming the smoke detector at the end might work, but that's not something you can do that conveniently.
posted by aubilenon at 11:36 AM on May 7

If you absolutely, positively want a detector in that location you can replace the smoke detector with a rate of rise/fixed heat detector. They're much less likely to sound in the presence of shower steam than smoke detectors. I can't recommend any one brand, so shop around.
posted by tommasz at 1:16 PM on May 7

doesn't a smoke detector know the difference between smoke and steam?

That's easy enough to test if you've got a kettle and an extension lead.
posted by Mike1024 at 2:13 PM on May 7

Thanks everyone. We don't have a bathroom fan, but I do crack the window open when showering. And I usually spend several minutes after showering drying off and applying my various lotions, hair serums, etc., so it's not like I hop out of the shower and open the door and a huge rush of steam comes out. I think the solution will be to just get a new smoke detector. The one in question isn't ancient, but it's probably a few years old and could stand to be replaced. Still weird that the closer alarm has never gone off, but maybe it's a little newer...
posted by LolaGeek at 3:56 PM on May 7

It doesn't necessarily depend on how close the alarm is, it could just be an issue of placement and air flow. You could move the one that's causing problems to another place in the hallway, maybe even the other side of the wall. I used to have this problem, even after replacing the alarm multiple times with new models. I ended up just pointing a box fan at it whenever I took a shower, and that completely took care of it.
posted by emilyd22222 at 11:51 AM on May 11