Half a croissant, on a plate, with a sign in front of it saying '50c'
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Unplugged metal-detector alarm

Rechargeable-battery-powerd alarm that sounds if someone walks through unplugged metal detector
  (+6, -1)
(+6, -1)
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Numerous times, it's been necessary to clear an airport because security personnel let passengers walk through metal detectors that weren't plugged in. While it might feel good to rant about the quality of those personnel, it would not be very productive. I therefore propose an alternative solution:

Affix to each walk-through metal detector an alarm which will sound any time someone walks through the detector but it is not plugged in. Passive IR motion sensors require a sufficiently-small amount of current that even a pair of AA batteries could power the thing for a month; given that the detectors are usually plugged in, rechargeables should work quite well for the application.

supercat, Mar 01 2002


       Nice.  Croissant.  How do the PIRs know when the metal detctor is not plugged in?
bristolz, Mar 01 2002

       The PIR alarm unit would easily be wired into the main power supply for the walkthrough unit. When the unit is plugged in and powered on, an electronic switch or relay would connect the batteries to the power supply to charge them while disconnecting them from the alarm. When the unit is not powered, the alarm would be enabled.
supercat, Mar 01 2002

       Very sensible. Little point in having a security system if it isn't switched on. I don't know how these things are wired in, but maybe you could have a time switch or something that's connected as part of the installation procedure to ensure there's an alarm if a unit isn't plugged in, that would be disabled for transit. Was it the cleaners pulling out the plugs to plug their vacuums in?   

       Alternatively, if all the security systems are connected to a central control unit, it should be simple for a computer to poll each device. Why isn't this being done?
pottedstu, Mar 01 2002

       Simpler solution: the metal detector should make some small sound of acknowledgement - a low frequency "boop" noise perhaps - any time someone passes through, whether or not any metal was detected, so you know it's on and operating. The sound would need to be something with a low threshhold of repetitive annoyance.   

       Of course it should also make the additional alert noise when metal is detected.   

       Then, if someone passes through and there's no "boop", you know it's not operating. Alternatively, it can 'boop' when no metal is detected, _or_ alert when metal is detected. Either way it makes a sound.   

       Even simpler... a "power on" indicator light.
waugsqueke, Mar 01 2002

       Yeah. There's a Dilbert-esque story about a manager who wanted a light on a device so the user could tell it was turned off. Makes much more sense to provide better indication that the unit is on and assume it is off otherwise. Put a big a$$ed flashing light on top and a big a$$ed sticker on the side that says "If the light's not flashing, the detector's not plugged in". Just proves you get what you pay for.
phoenix, Mar 01 2002

       Or it could have spring-loaded doors that close when the power is off. 'Course, this wouldn't seem like such a fine idea to the guy going through it when a power failure hits.
beauxeault, Mar 01 2002

       Metal detectors HAVE "power-on" lights. Many of them also make a very soft confirmation beep as people walk through. If the guards at airports were of high quality, these would suffice. Given that some of the guards seem to be less than brilliant, however, an alarm whose sounding would be unmistakable to other passengers may be useful.   

       BTW, as for a spring-loaded door, I thought about that. It wouldn't have to be a high-security door since even a really stupid guard should notice someone trying to climb over a barrier. Nonetheless, it would be considerably more complicated than a simple alarm and if the guard is even remotely alive the alarm should suffice.
supercat, Mar 01 2002

       I guess indication is not strong enough. Have the detector open a door at the end once it detects that someone walked through it? An unplugged indicator simply wouldn't let people in.
jutta, Mar 02 2002


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