The FA-I-CCA-D1 (single temperature) with Voice Message will hold up to 3 numbers and is set up for quick status such as when the temperature gets out of range, the power goes out, or if the back-up battery needs replacing. (Model A) The FA-D2 (dual temperature) monitors the temperature, the power status and an external contact. It also offers remote switch control capability. Upon an alarm condition, the FA-D automatically dials up to three phone numbers with a voice message. Current temperature and alarm conditions can be checked by calling from any remote location. (Model B)