# Can a trigger a motion sensor light by turning on a porch light? **URL:** \ **Category:** Factual Questions\ **Created:** [November 7, 2019, 1:20pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119 "2019-11-07T13:20:32Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 7, 2019, 1:20pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/1 "2019-11-07T13:20:32Z")
What I would like to do is mount a couple of solar powered LED lights deeper back on my property. Solar because I don’t want to run wires to these far places. But I would like them to come on when I flip my porch light on. If I aim the motion detectors at the porch lighted area and light itself, would that typically and reliably trigger a motion sensor light to come on? ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [November 7, 2019, 1:45pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/2 "2019-11-07T13:45:41Z")
Probably. Motion sensors in lights typically work by detecting changes in the light and shadows in its field of view. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [November 7, 2019, 1:47pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/3 "2019-11-07T13:47:23Z")
The motion detector lights I’ve got mounted on my house sense moving heat signature. The sensitivity is somewhat adjustable, but since your porch light is not moving, I’d say it will not work. I’ll also note that they are more sensitive to heated objects moving across their field of view rather than directly to or away. ---
**Author:** ![DCnDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dcndc/32/2842_2.png) [@DCnDC](https://boards.straightdope.com/u/DCnDC)\ **Post date:** [November 7, 2019, 1:56pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/4 "2019-11-07T13:56:37Z")
After doing some research, it appears to depend on exactly what type of motion sensor your lights use. Some work by detecting changes in light, others work by using an infrared beam, or radio waves, or microwaves, or a light beam, visible or non-, or a combination of any of the above. If you have the type that detects changes in light, you’re likely good. If your lights use one of the other methods, probably not. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [November 7, 2019, 2:06pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/5 "2019-11-07T14:06:38Z")
> [@kanicbird](#): > > Solar because I don’t want to run wires to these far places. I have not had good experience with Solar yard lights. The batteries go weak, the lights are not that bright and the plastic enclosure is sensitive to rain / sunlight. Of course, there maybe better quality solar lights and my experience is based on the solar lights from Costco. I think it is worth the effort to run low voltage cable and install quality outdoor rated lights in metal housings. In the long term, they have a better payout. Nothing against solar power. You can install yard solar panels, if you like going that route. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 7, 2019, 2:16pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/6 "2019-11-07T14:16:43Z")
I don’t think you are going to be able to trigger any decent motion sensor this way. As for solar lights, I had excellent results with [these](https://www.amazon.com/dp/B00H261H98/ref=cm_sw_em_r_mt_dp_U_xCcXDbM786KDE). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 7, 2019, 3:01pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/7 "2019-11-07T15:01:47Z")
Even if you set up a system that works that way at that start, motion sensor lights are very erratic and unreliable, and get more so as they age. The one on my mom’s driveway light sometimes triggers on a cat or a squirrel, but not on a group of humans walking past, for instance. There are probably lights that you can get that can be controlled via WiFi. And if you don’t want those (there are some security issues with them), then you should just bite the bullet and install wires. Wires are simple, reliable, and long-lasting. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 7, 2019, 3:07pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/8 "2019-11-07T15:07:20Z")
Most motion sensors use [passive infrared (PIR)](https://en.wikipedia.org/wiki/Passive_infrared_sensor) sensors. Those would not respond to changes in visible light. Some use microwave (radar). Those would not respond to any change in lighting. Some motion-activated security cameras rely on the camera and detect movements seen by the camera. Those may or may not respond to a lamp being turned on - depending on how the software is set up. (And you won’t find lamps that use this technology anyway, it’s used on security cameras only because they already have cameras, and video analysis software is cheaper than a separate motion sensor.) There are [other technologies](https://en.wikipedia.org/wiki/Motion_detector#Sensor_technology) but usually, they design motion detectors to respond only to actual movement, and **not** to respond to changes in lighting. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 7, 2019, 3:13pm UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/9 "2019-11-07T15:13:55Z")
Many solar lights have a photo-sensor to turn them off in the day time so turning on a porch light might turn those lights off. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [November 8, 2019, 12:48am UTC](https://boards.straightdope.com/t/can-a-trigger-a-motion-sensor-light-by-turning-on-a-porch-light/843119/10 "2019-11-08T00:48:52Z")
> [@kanicbird](#): > > What I would like to do is mount a couple of solar powered LED lights deeper back on my property. Solar because I don’t want to run wires to these far places. I’d suggest you just bite the bullet and run the wires out there now. My experience is that you will eventually have to do that anyway. And it’s actually cheaper then what you would spend on solar panels, wi-fi lights, etc. You can easily get direct-burial electrical cable, and that only has to be buried a foot or so down. And it’s not much more expensive to get 3-wire cable, so one line can be always live and the other can be switched from inside your house. This also lets you install a regular outdoor outlet there – and everyplace I’ve installed one of them, I’ve eventually found it very useful.