As I said 7 lights, 4 on the front and 1 for each man door which is 3. What I am looking for is, if I walk up to any side of the garage at night with motion detection added on I want all 7 lights to go on. Each light will have its own motion detection unit added on, and connected to the rest. Or would a single photo cell wired across all 7 so at nite the garage lites up. Will be using LEDs in each of the single bulb exterior lights. Can this be done to have all the lights turn on with only 1 motion detection unit added to one light or all 7 lights? Even though all lights would have their own mini motion detection unit added and mounted 3 to 4 feet lower than the light fixture.

  • What make and model of lights are you dealing with here, or have you yet to purchase/install them? Commented Nov 3, 2019 at 20:18
  • Did you ever get this resolved? If so, please give a check-mark to the answer that helped you the most, or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer
    – FreeMan
    Commented Jul 31, 2020 at 17:24

1 Answer 1


Yes, you can crossover motion detectors if you set it up properly. You would use discrete motion sensors and lights, not combo light-sensor units. If you're married to the idea of combo units, you will need to "hack" them, which is off-topic here.

All motion sensors have day/night detection, and will not activate in daylight.

  • However, motion sensors's light level detectors read absolute lux (the human eye cannot see absolute lux; the eye auto-adjusts to ambient light; sensors can't/don't/don't need to). Light sensors are programmed with defaults for the lux of day vs night. In very shady locations, or locations with a high level of artificial light (e.g. in the bask of a street light), those default values will fool the sensor. However after it experiences a couple of day-night cycles, it will calibrate to the appropriate lux levels. Thus, do not angrily think "what is wrong with this thing!?" until day 3. However, if you cut power to the sensor, you wipe its memory and it must start over so having it downstream of a light switch etc. is a bad idea.

So to wire this, you must

  • bus a white wire from supply to every sensor AND lamp (netural)
  • bus a red wire between every sensor and lamp, but no need to go to supply (switched-hot)
  • bus a black wire from supply to every sensor (no need to take it to the lamps), this is supply hot.
  • Do not put a light switch on a black wire.
  • At the lamps, connect their black wires to the red wire.

You can use /3 cable for this.

  • And now I'm about to frustrate you with some left out details...the lights are already bought and they do not have any sensors on them, just one bulb fixtures. To accomplish this I think I understand you to say I need to buy 7 discreet motion sensors to add to each light with the wiring you described. I have looked at all the big box stores for add on sensors, and they are huge. Where could I find discreet small motion sensors? Up here in Glens Falls there are a number of electrical suppliers, probably a good place to start. Thank you for your patience.
    – Cabover4us
    Commented Nov 4, 2019 at 5:58
  • Well, with a little more work and wiring @Cabover4us, you could keep the lights you already have, wire them on a mains wiring string, then run a separate 12V system for the sensors. 12V sensors are both smaller and cheaper, but would need to be wired separately with cheap/easy phone/thermostat style wiring. Then use a relay to actually turn on the lights. Commented Nov 4, 2019 at 6:09
  • Thank you very much for the advice, I will check on 12 volt sensors..
    – Cabover4us
    Commented Nov 5, 2019 at 10:55
  • Late to the party, but 1 sensor should work just fine on the front of the garage, even though there are 4 lights there. The light/motion levels are probably not significant from one side of the front of the garage to the other side. You might possibly need 2 sensors if you have <person door> --- <garage door> -- <garage door> a sensor by the person door may not detect a car aimed at the far garage door, and vice versa.
    – FreeMan
    Commented Apr 2, 2020 at 17:39
  • Let me see if I'm on the right path? I have 7 - 120 volt exterior lights with LED screw in bulbs coupled all together in series plain lights with no sensor included. Second electrical circuit consisting of transformer 120 volt reduce down to 12volt energizing 7 small 12 volt motion sensors and these connected to 7 separate relays. When motion is detected anywhere around building, the 12 volt sensors, anyone of which will activate one of the relays which sends 120volt to the 7 lights in series circuit of lights. I realize I wrote this rudimentary but you get the drift.
    – Cabover4us
    Commented Aug 1, 2020 at 19:06

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