For sharing information purposes especially those who are using notebook, here is a sample device which detect notebook in a hidden place (i.e. in a car). 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".