Does Heat Trigger Motion Sensors? Cold Weather Motion Light

Does Heat Trigger Motion Sensors? Cold Weather Motion Light

It depends on how motion is detected. Most passive motion detectors look for changes in infrared radiation, aka heat. When you come into the range of the detector, it will sense your body heat and trigger the alarm. More specifically, it looks for changes in heat. As such, any sudden source of heat will also trigger the sensor. That includes turning on a heater aimed at the sensor, and yes, light, if it is bright/hot enough. Note that most infrared sensors warn you that air current, i.e. opening the door, can trigger it. That’s due to the sudden temperature change.

There are other types of motion sensors. Many hidden cameras, and even your cellphone, can be programmed to constantly take photos. If the camera is held still, and there are differences in successive photos, then the motion can be inferred. In most cases, the camera would then begin to record video. If it is no different then the older photo is deleted to save space. Such sensors would not work in the dark since there would be no images to compare. And turning on the light from complete darkness should trigger the sensor since there would be a dramatic change between the dark image and the lit image.

Some passive sensors are more exotic, detecting electrical fields. They operate like the capacitive touchscreen of your smartphone or the touchpad of your laptop, except that contact isn’t needed. One advantage to these sensors is that they can work through many surfaces, i.e. walls and doors. Similarly, you can place a piece of paper between your fingers and touchscreen, and your fingers would still register. Some travel alarms, designed to hang on the doorknob, work this way. Fake dog barkers also use this technology. When movement is detected outside your door, recordings of a fierce dog barking are played to scare away potential criminals. Such sensors are not affected by turning on a light.

Then you have active motion sensors which emit a signal. One example is the photodetectors used in elevator doors and some alarm systems, like the ones that beep when someone enters a store. Essentially, it looks for changes in ambient light. In the elevator, a source emits light (usually infrared) which is detected by the door. If the light beam is broken/blocked, the alarm is triggered. These would probably not be affected by turning on the light since the sensor is tuned specifically to only react to the source light.

Then there are sensors that detect reflected ultrasonic sound. These are essentially radars, copying the way bats detect motion. A source emits sound and the way the sound is reflected back can indicate motion. Fetal ultrasound is such an example. It can be used to capture motion like a fetal heartbeat. More sophisticated systems will even use Doppler to detect the direction and speed of motion. These would not be affected by turning on lights.