There’s much of the electromagnetic spectrum that we cannot see. Like how LED wristbands are triggered at concerts or how to identify someone at DEF CON in a crowd of cellphones and electrical devices. Eric Escobar of SecureWorks provides some really clear analogies to help anyone visualize the differences between NFC, Bluetooth, and Wi Fi such as how your router and your microwave are both 2.4GHz - the difference is the number of watts behind each signal.