These are the tones that are heard when buttons on a telephone are dialled. These tones are used by telephone networks to send messages over a telephone connection. They are also used by devices such as fax machines, care alarms, burglar alarms and textphones to communicate over ordinary telephone lines. Tunstall's proprietary alarm protocols TTNew/TT92/TT21 all use DTMF as a means of signalling. DTMF specifically sends messages in pairs of tones that are transmitted simultaneously. By comparison, STMF transmits single tones at any one time, this tends to provide a more reliable transmission compared to DTMF. STMF is a proprietary Tunstall technology.