The transceiver was found in the cockpit by Jack, Kate, and Charlie. ("Pilot, Part 1"). Sayid tried to use it to send a distress signal, but instead they received a French distress signal with a counter following the message saying how many times it had been repeated. Shannon, who possessed a passing familiarity with French, translated the message, and Sayid concluded that the distress signal had been playing for 16 years. ("Pilot, Part 2")
Notice the hole to the left of the keypad.
The prop used in the show is likely a RHP-520, manufactured by Rexon Technology Corp. of Taiwan. The only noticeable differences between the two devices are logos on the below the LCD. The Rexon labeled radio reads "REXON RHP-520", whilst the model seen in Lost has the words "SLS ABT-520". Additionally the text displayed on the screen of Sayid's transceiver is simulated; the RHP has a much more crude display whereas "Acquiring Signal" on Sayid's is very sharp.
Sayid looks for a signal.