I set myself the challenge of building a cheap low cost laser warning system for practical detection and warning of police speed laser. I don’t have the right components to hand at this stage. But the principle I show here is essentially the same as what I will build later.

In practical terms you cannot see police infrared laser with the naked eye. Police speed laser guns operate at about 905nm. So actually using a laser pointer is a nice visible demonstration of how the system will work.

The response of the system is also pretty quick. If I take a photo of the setup with the camera flash, the camera picture already shows the flash is detected and the red LED isilluminated. Thereby if the police cannot get an immediate lock on your speed in the first zap, and they need a second reading (as is quite common), such a system can give you enough practical warning to do something about it to prevent a ticket, or reduce the size of the penalty.