Spy bugs and tracking devices are not only very popular in the DIY community. There are hundreds of shops out there selling equipment like this for outrageous amounts of money. This little circuit costs less than $ 2 and is exactly what you would get from those ‘professional’ spy equipment stores.
This circuit is nothing more but an unformulated Butler oscillator. C3 can be used to adjust the frequency. My circuit could be tuned between about 100 and 150 MHz. The frequency is, however, not very stable. Many outside factors such as supply power will change the frequency rapidly.
In my opinion, the performance of such a circuit is pretty much useless for the tracking of a person / object. The frequency is unstable and the range is fairly low. Most spy shops would charge you a lot of money and claim that this is the same stuff they allegedly sell to the government.
Why am I posting this? To warn you, don’t buy stuff like this. If you absolutely want to try it, build this simple circuit yourself and throw it away once you realize how useless it really is.