or....
You are correct, and therefore, it should be a simple matter of using an electronic "sweeper" device on your vehicle to detect the outgoing signal. You can then presumably do with it as you will, seeing as once it is attached to your vehicle (your property) it becomes part of that vehicle, and thus is yours.
A criminal has to be sentenced by a court before he can be required to wear a monitoring bracelet. This is nothing more than a monitoring bracelet for your car, and thus you deserve all the protection of the law in order for the cops to be allowed to legally attach one to your car. If they don't give that to you, then they have merely made a present to you of a (presumably not cheap) GPS tracking device.
or....