By using PicoScope with the Keyless entry signal carrier detector (TA330), a sensor with a three-meter-long lead, the technician can detect the presence of a keyless entry carrier signal in the frequency range of 125 to 140 kHz (which is used by most manufacturers). The device has a short range by design, allowing the technician to check each pick-up coil in turn to identify faulty units.
Note: The detector does not pick up or decode the high-frequency secure information used to unlock the vehicle. It only displays a waveform of the signal on the screen.
You can find the keyless entry signal carrier detector here.