What: The normal defensive technique of going into airplane mode and switching off Wi-Fi will halt most mobile detection systems. But one approach can find you another: through Bluetooth.
Deployment: One retail mobile tracking company, LoyalBlocks, is using Apple's Beacon system to detect any phone — even in airplane mode, with Wi-Fi turned off — if its Bluetooth is enabled. Once detected, it can identify the phone and you. It could also track Bluetooth before Apple's Beacon, but Beacon makes it even easier.
Protection: Turn phone off.