The PHR04 RF Keychain Remote is programmable to any 2 sequential X10 addresses (requires transceiver). Individual RF components can be added in nearly any combination for customization of each installation. Multiple RF Remotes can transmit to a single Base Transceiver (PAT01). Only one Base Transceiver is needed per addressable letter code (A-P). A second may be added if more than one letter code is used.