Bluetooth
Bluetooth is a wireless technology for communicating with other devices over short distances (e.g. headphones, car media).
A Bluetooth enabled device can scan for nearby Bluetooth devices. Devices are identified by a Bluetooth device name. To enable secure connections that do not require user intervention (e.g. just by getting in the car) the Bluetooth devices must be “paired”. Pairing is normally required only once.
Many devices support Bluetooth LE which is a version of Bluetooth that requires very low power and hence battery use.
NFC
NFC (Near Field Communication) allows communication between two devices like a phone and a credit card, typically within 4cm.
It is fascinating to think that a contactless card (e.g. credit card) has a basic processor and memory – but no battery for power. The phone generates an electromagnetic field and the card gets its power from this field (electromagnetic induction between loop antennas). Once powered, they can communicate and securely exchange data.
Phones typically indicate an NFC card is in its proximity by a notification beep.
IR
Some phones can send infrared signals to allow a phone to be used as a remote control (for example as a TV remote).