Bluetooth pairing and NFC on mobile devices for A+ Core 1
Bluetooth pairs two devices once, after which they reconnect automatically until one is unpaired. Pairing may ask you to confirm matching PINs or enter a passcode, commonly 0000 or 1234. NFC needs no pairing: it works by a tap at up to about 2 cm, and the reader can power a battery-free tag.
Pairing a Bluetooth accessory
Google's Android help says that after you pair a Bluetooth device for the first time, the devices can connect automatically, and they stay paired until you unpair them.
If the phone asks for a passcode you do not have, Google says to try the most common ones, 0000 or 1234.
When pairing a phone with a car from the car's screen, Google's steps say to check that the PINs shown on the phone and the car match, then tap Pair, Accept or Confirm. Matching PINs confirm you are pairing with the right device.
When pairing fails
Apple's steps start with the basics: keep the accessory close, put it in discovery mode if it has not been paired before, turn it off and on, and make sure it is charged.
If the accessory was previously connected: unpair it, put it back in discovery mode, and pair again.
If the accessory pairs with some devices but not the phone: unpair it from the other devices, then try the phone again. Only after that does Apple suggest asking the accessory maker about compatibility.
For a car that will not pair, Google says to forget the car on the phone and clear the phone from the car's memory before pairing again.
NFC
The NFC Forum describes NFC as contactless radio at 13.56 MHz with a typical range of up to 2 cm. One side can transmit power, which allows battery-free tags.
Card emulation mode lets a phone act as a contactless payment card or transit ticket. Reader/writer mode lets a phone read tags holding web addresses, contact information or automations. Peer-to-peer mode lets two devices touched together exchange data, such as their users' contact details.
The NFC user experience is built around a tap. There is no pairing step and no network connection.
Where the exam catches people
Believing an accessory that pairs elsewhere but not with the phone is incompatible: first unpair it from the other devices and try again.
Believing a Bluetooth passcode is the phone's lock code or SIM PIN: if it is unknown, try the common defaults 0000 or 1234.
Believing the PIN prompt during car pairing should be typed in: when both screens show a PIN, check they match and accept.
Believing tap-to-share between phones needs Bluetooth pairing: NFC peer-to-peer mode exchanges data with a tap and no pairing.