Here is a smart gadget that detect and track hidden Bluetooth card skimmers, which are often used ATM, gas pump, and vending machines. The BlueSleuth Bluetooth Skimmer Locator from Berkeley Varitronics Systems has a direction finding antenna which helps you find criminals and the devices they use. It has a range of up to 75ft indoors and 1/4 miles outside.
This gadget can also used to find unauthorized microphones, smartphones, and earpieces. Comes handy for TSCM teams. More information is available here.