The Protek JCB01 1200/75 modem, made by Cirkit of England, is an acoustic modem designed to transmit and receive computer data over standard domestic telephone lines. 

Supporting baud rates of either 1200/1200 or 1200/75, it allows users to exchange messages and programs between computers as well as access online databases using the international 1200/75 baud standard. 

The modem requires four AA sized batteries; two are housed in each end of the unit. This battery power provides up to 40 hours of operation.

The modem works with any standard or TTL-level RS-232/423 interface capable of split baud rates, though it's not compatible with the ZX Spectrum's Interface 1 RS-232 port. 

Cirkit also produced interface packs for popular home computers of the time, including the BBC Model B, ZX Spectrum 48K, Commodore 64, Oric/Atmos 48K, and Acorn Electron. 

Our model has a serial number of S/2644/3/E/62286 and is complete with the instruction manual. This is in excellent condition and was kindly donated by Keith Godber.