How to test Remote Key Transmitter?

Hello,

The remote central locking my car has not been working. There are 2 main components. The reciever unit which is located in the trunk and the transponder unit which is on the key. The reciever unit recieves the signal and then sends a voltage through the wires to the door lock solenoids to lock/unlock.

The Key transmits the signal to the reciever unit. Both the key and the receiver unit are equipped with a ROM chip that has an identical code.

I know that there is no severed wires from the reciever unit to the door locks as I can manually lock/unlock the door by shorting the pins out on the connector.

I bought a replacement reciever unit off ebay supposed to be working and still did not solve the problem. At this point I am suspecting it's the transmitter on the key so I began to test that.

When I pressed the button it draws voltage from the battery in it, so this demonstrates that something works inside the circuit, but I am not sure that the signal is being transmitted. How would I test if the signal is being transmitted?

I don't know the frequency, but I think it should be around 300 or 400mhz as this is the frequency these devices commonly operate on.

Any suggestions would be great. Thanks.