• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Device to Trigger Radar Detector

Not open for further replies.


New Member
I don't know how some of y'all will feel about this, but I'm looking for a small device that will trigger a speeding car's radar detector.

I guess I'm tired of being run off the road by cars driving 95mph in a 70 or 55 zone, and it would make me happy to hit a button and watch them slam on their brakes in a panic.

I thought I saw a kit for this once, or maybe a completed device. However my searching through google has me coming up empty.

Any ideas on this?


Active Member
I feel much like you do about the bad drivers but what little I know about the radar detectors is that they are somewhat intelligent and I would not expect them to be triggered by a simple transmitter - the transmitted signal must be modulated to "look like" something from a speed measuring device. My guess is that whether simple or sophisticated what you want to do is illegal. I recall reading about the various FCC rulings that disallow police to run radars for the sole purpose of triggering detectors. I notice that in Pennsylvania they seem to get around this by setting up the speed measuring/display units that are supposed to tell you that you are going too fast - but they turn the sign off and just let the radar run - triggering detectors so often that users turn them off.

Remember that these radars run at microwave frequencies so the electronics challenge is significant. You'd either have to skillfully generate a fixed and appropriately modulated signal at just the right frequency or generate something with enormous power that is more likely to hurt you than slow other drivers down.


New Member
A detector consists of a a simple SHF reciever.
These are usually relatively simple circuits containing a microwave detector (often based upon a Schottky diode) and a comparator that drives an alarm. Such devices will pick up any microwave signal between two and ten Gigahertz so they cover most but not all speed camera's avaiable.

The method of speed determiation in police equipment uses the doppler shift principle, that is the phase change in the returned signal from the the transmitted reference. Unlike proper RADAR the outgoing signal is unmodulated, generating the signal is often just a case of powering up a Gunn diode fitted into a resonant cavity with a horn antenna to give a narrower beam.

A simpler solution, aside from mounting an unshielded microwave oven in the trunk of your car, is a second brake-light switch.
Works wonders for tailgaters! :twisted:

I understand that radar detectors are legal in the states, wonderfull bit of salesmanship that was.... :lol:
You see, the average reaction time to put the foot on the brake is half a second [0.5sec] whilst a quick read of the sales blurb for speed cameras reveals that they stabilise and capture the cars velocity in around one-tenth of a second [0.1sec]. Basically the buzzer gives the driver no warning just sounds to let you know you've been busted.

The penalty for interfering with the operation of speed camera varies but rest assured using any form of electronic jamming by accident or design could well prove unpleasent in a court of law. :cry:
Not open for further replies.

Latest threads

EE World Online Articles