Here is a sample device which detect notebook in a hidden place. For those who have never heard of it, attached below are the pictures of the detector.

Even with the WIFI (wireless), Bluetooth or the entire notebook is completely off, it can still be detected via radio frequency. Therefore never leave your notebook, PDA (Personal Digital Assistance) , mobile phone or any valuable electronic devices in the car. These devices are not expensive, it costs less than RM50 for the thieves to start the business.