Yes, aluminum foil will block security tags. Therefore, it is often used to block sensors from catching signals sent by anti-theft devices. The primary reason is that several layers of aluminum foil can block radio signals. It gets creative with special bags lined with aluminum foil to avoid detection at the cashier. The bag looks very ordinary on the outside. Still, the aluminum foil lining gives it a superpower to pass through the anti-theft detector without turning it off. In the U.S., the average thief walks out with $438 per theft, and the chance of being caught is only 1 in 48. If you're a severe retailer, you can't ignore it.