Radio frequency identification, or RFID, is a common method of near-field communication. You can teach your Raspberry Pi to understand an RFID board's communication with RFID cards and keyfobs.
There are a few different RFID kits available. I used the Elegoo RC522 included in their kit, which is a fairly typical RFID board. Adafruit also has kits that detect both RFID cards and NFC signals typically used on smartphones, and they always include great instructions. You'll also need a red-and-green LED and a couple of 330-Ohm resistors. Finally, you will need SPI enabled on your Raspberry Pi Zero; if you haven't done that already, refer to Basics of SPI and Setting up the SPI Module in Chapter 5, Getting Your Hands Dirty Using the GPIO Header.