What is that Ceiling Gadget?

[consumer]

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I was just curious what these gadgets are on the ceiling that I see everywhere and what do they do.  These ones are from the one in my gym, but I see them everywhere schools, restaurants, bathrooms, shops, etc.

Also are they available for purchase somewhere or for private businesses only?  Thanks.

[cat fud]

These are Passive Infra-Red (PIR) sensors.  They are used to detect people moving in an area.  If they detect a person they send a signal somewhere, maybe a burglar alarm, maybe a heating or lighting controller.  Often you can see them working- a small red LED will light up when movement is detected.  You may also see tiny versions of these on the lamps in the common areas of your apartment building which turn the lights on when you walk by.

[consumer]

okay thanks for the reply, now I am less nervous when I feel one of these things staring at me when I am using the restroom :'(.   I do have to say I've never seen the red light you speak of coming from it even when I am jumping up and down in front of it.

But this does seem useful especially since I have had many disturbances outside of my apt; drunks, attempted vandals, and I think a spurned girl who mistook my apt for the apt of her ex or something by the looks of the kick marks on my door.

Can these be purchased by individuals or public entities only? Perhaps at your local friendly E-mart? Thanks.

[cat fud]

You can buy standalone units, battery operated.  Some will light a lamp, some will sound a chime.  It depends on exactly what you want.  I suggest you go to DealExtreme.com and search for 'PIR' to get an idea of what sort of devices have PIRs in them.

The red LED I mentioned is not present on all units, and sometimes it's used for testing/setup and turned off in normal use.  Either that or the units you have seen are not connected to anything :)

[Paul]

These are common the world over. The red light is either very faint so not visible unless the lights are off or turns on when the thing is "active". If you've ever been an office worker in a standalone building, you're likely familiar with them. The first in or last out at a business gets the (mildly stressful) task of whacking in their PIN (or if leaving, getting away from the keypad and out the door after doing so) before the red light has been on too long. If not, you get one of those wonderfully embarrassing encounters where you have to apologise for wasting security's time. :D