Why does Your Radar Detector Go Off Near Supermarkets?

There's a relatively new use for radar, and you've probably experienced it many times, and possibly in a couple of ways, without even knowing it! Those automatic doors at many supermarkets and stores are now using a form of radar to detect the presence of shoppers!

I know many of you are thinking that those doors have been around for a long time, and while they have, the tech behind them has changed over the years. Some still use the old standard of a pad in the floor to detect when a person approaches, which, while initially effective, can cause a lot of false readings, which makes the door open and close repeatedly, and in areas with inclement weather, such as Chicago, snow can render them almost useless.

To combat these issues, automatic doors have been upgraded in recent years to use similar technology to a radar gun. Many doors now send out a radio wave, which, if something moves in it's vicinity, changes frequency, and the change tells the door to open.

Unlike a baseball radar gun, which takes a precise measurement of the radio wave frequency to see how fast an object is moving, these radar doors simply wait for a significant enough change to open. The power is set fairly low, and the sensors are not as sensitive as police radar, as the door shouldn't open when a fly zips by or if someone walks past the door at a distance. The angle is also calibrated fairly specifically, with the sensor on the top of the door aimed down. If it aimed straight out the radio wave might bounce back from a great distance.

I looked into this because the other day the radar detector in my car when off when I was in the parking lot of the local supermarket. I looked around and didn't see a cop car anywhere, and the detector only when off when I drove past the front door. It was fairly weak, but it still registered. I'm going to look into whether the same thing is what some traffic lights use to sense if a car is waiting. Stay tuned for more posts in the coming days/weeks.

Labels: radar detectors, radar technology