Redcare is a widely deployed standard from BT, used in the UK to allow alarm systems to be continuously monitored from an alarm provider's "Alarm Receiving Centre". Installed correctly, the system can be part of a system compliant with EN50131 Grade 4, the highest security grade in the European Standard for Intruder Alarms. The basic system involves transmitting a continuous signal on a standard phone line, which can also be used for normal voice and broadband services, to prevent alarm systems being defeated by the line being cut. Enhanced versions exist that also use GSM (mobile) as a backup to the main phone line or that can function using either ISDN or IP as the primary connection.
Although early Broadband deployments in the UK were incompatible with Redcare, this problem has now been resolved. Redcare works below the voice frequency spectrum on a phone line and therefore does not interfere with phonecalls or ADSL (which uses frequencies above the voice spectrum).