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Stop false alarms

Discussion in 'General Electronics Discussion' started by The Baron, Jun 12, 2017.

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  1. The Baron

    The Baron

    Jun 12, 2017
    Does anyone know of a company who make an add-on pulse counter to tame false alarms from motion detectors, such as a bird flying past, etc?
  2. Alec_t


    Jul 7, 2015
    Welcome to EP!
    I can't help with the pulse counter, but I tamed my PIR sensor somewhat by putting a strip of reflective foil inside the lens part to restrict the angle of sight so that only bodies above a certain height would trigger the PIR.
  3. Externet


    Aug 24, 2009
    False alarms are the headache of all security providers, as bring them out of their 'comfort zone' reading newspapers, having coffee, chatting and perhaps napping waiting for the phone call to act. False alarms are fought with past experiences and location/equipment used.

    I would say an 'AND' system should work better : Detection A AND detection B should be active to trigger an alarm. So, well thought redundancy is the way I would go after, using different sensing schemes simultaneously.
    Any security company headed by a brain should be capable of implementing near fool-proof diverse redundancy.
  4. Bluejets


    Oct 5, 2014
    Get a sensor that has a sensitivity adjustment and is good quality.
  5. The Baron

    The Baron

    Jun 12, 2017
    All good suggestions, but sometimes the best laid plans: etc etc. I used to purchase a pulse counter that would count the number of times a motion trips before it would open the circuit on the panel. Worked great on old systems, without having to spend money on new sensors. If anyone hears of a device like this, please let me know. Thanks!
  6. Bluejets


    Oct 5, 2014
    All well and good to add an "N" counter but what terminates the counter?
    I think you are going to have to go with a 1 of design, perhaps an Arduino or similar for simplicity.
    Apart from that, most sensors are mounted around 2.4m AGL and face the ground so birds are not normally an issue.
    Last edited: Jun 13, 2017
  7. ChosunOne


    Jun 20, 2010
    Baron, it really helps the process if you share what kind of equipment you're working with (Brand and model numbers are great) and, in this case, what you're trying to do with it. Since you mention birds flying past, I can infer you're attempting to sense motion outside somewhere, although without more information, I can't rule out the possibility that your pet bird gets loose inside you house sometimes.

    Most PIR (Passive InfraRed) motion sensors have built-in pulse counting these days, but since you didn't mention what kind of sensor you're using, I won't bother to elaborate more on that. Motion sensors also come in MW (Mircowave) and US (ultrasonic) flavors; and PIR & MW "dual-tech" sensors are common. PIR and US dual-tech used to be common decades ago, but they're all but extinct now, at least in North America; but again, I can't rule out the possibility that you're using old equipment. Some people refer to Active Infrared (a.k.a. "electric eye" beams) as motion sensors.

    whatever you're using, I have my doubts that adding pulse counting will prevent your system from seeing birds flying past. "Pulse counting" in the alarm industry is used to refer to how many zones in the coverage area of a motion sensor are tripped in a brief time window---it's useful to eliminate very localized phenomena, like a stationary heat register heating or cooling rapidly, or a mouse moving within a very limited space; but a bird flying across the coverage space of a motion sensor is actually very close what the device is designed to detect: It's significant motion within the sensor's coverage area.

    If you're trying to use pulse counting in a different sense, e.g., how many times the sensor trips in a brief time window, that will cut down the number of false alarms but it may also cut down the number of real alarms. Alarm equipment manufacturers have been working for decades on motion sensing equipment that will detect motion only from intruders, but still detect intruders, even ones who creep slowly across the coverage area. It's not easy. Again, I don't know what you're trying to do, so I won't elaborate more on that. It may be irrelevant to your purpose.

    If you're trying to detect motion in the great outdoors, but only motion of humans or cars or whatever; and you want your sensor to ignore bats, cats, rats and brats, dogs, birds, possums, raccoons, deer, elk, moose, windblown papers and leafy branches and plastic shopping bags, coyotes, lizards, squirrels, flying fish, jumping dolphins, horses and cattle, butterflies, moths and grasshoppers, elephants, dangling/floating spiders, etc. ad naseum, then good luck with that.

    On the other hand, if you're just trying to eliminate/reduce falsing from small creatures, that's easier. The real problem with small creatures like small birds, squirrels, bats, cats and rats, is that when they're close to the motion sensor (whatever kind it is), they look big. A bird right smack in front of a PIR/MW/US/etc "looks" as big as a horse: In the case of a PIR, the bird changes the mosaic IR pattern the sensor is assessing as much as a horse does across the driveway. With a MW or US, the bird reflects as much radiation or sound as the horse.

    The simple solution, in that case, is what Externet suggested, although I'm going to phrase it more in alarm tech terms: Use two independent sensors--I usually recommend PIR, but the principle applies to all types--and place them so they're covering the same target area, but from widely separated vantage points. This will be limited by the range of the devices, but generally, farther away from each other is better, so that a bird (or squirrel, bat, rat, raccoon, etc) that looks like a horse to one sensor will look like a bird to the other. Depending on the setting, a separation of even a dozen feet might work. Using this configuration has solved a LOT of chronic falsing problems for me.

    I don't know how your motion detection is configured, so I'll just say that you have to wire the relay contacts to your alarm loop so that both sensors must trip in order to trigger an alarm. In nearly all alarm systems the detection loop of an intrusion zone is a closed loop, i.e., causes an alarm when the loop opens. If that's your case, then wire the alarm contacts of your sensors in parallel. If you're using an open loop (alarms when it goes closed), then wire them in series. Most motion sensors, when they're tripped, engage relays for a couple of seconds, which is plenty of a time window for detection of a real intrusion (or whatever you're trying to detect).
    (This is REALLY easier when I know what equipment you're working with and what you're trying to do.)
  8. The Baron

    The Baron

    Jun 12, 2017
    I have two applications for this counter. 1) To simply tame sensors in harsh environments, and 2) To help to fool proof a new device I am building that dispenses red pepper spray upon sensing a burglar. Our intent here is to stop the smash and grab thief.
  9. Bluejets


    Oct 5, 2014
    Harsh environment taming could cover many possibilities.
    So the burglar is only going to get a squirt of red pepper after "n" items are stolen?
    I'd be checking the laws over your way as I suspect that you could leave yourself open to law suits with the red pepper spray idea.
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