Caller ID signaling is sent by the local phone company's central office in either of 4 different electronic formats. Belcore 202 signaling is sent between the first and second ring in the countries such as the US, Canada, Mexico, Australia and others. Caller ID is sent before the first ring by British Telecom (BT) in the United Kingdom. Similarly, Caller ID is sent before the first ring or after a very short ring burst using ETSI signaling that is prevalent in eastern and northern Europe. In countries or regions where older central office equipment is used Caller ID is delivered via DTMF (touch-tones). Contact CallerID.com for a different version of this unit if Caller ID is delivered via DTMF signaling.

This unit is capable of capturing either Belcore 202, BT, or ETSI Caller ID signaling.