Quantity   Component name
1 × Raspberry Pi 3 An older model will probably work just as well. Loaded with Raspbian and powered, connected to local LAN.
1 × 315MHz Transmitter Referenced as WRL-10535 SparkFun and TWS-BS-6 in docs - $4
1 × 315MHz grounded outlet receiver with keychain remote Defiant 1 Outlet (Home Depot) or GE 18278 (Amazon) - about $20
1 × (Optional) Software Defined Radio (SDR) for testing. I used an RTL-SDR.com one from Amazon