In a typical alarm system within a building, such as a fire or burglar alarm system, many types of sensors, detectors, lights, strobes, sounders and other associated devices may be located throughout the building as part of the system. Groups of these devices are often wired together along a pair of lines serving the communication and power requirements of the devices. A group of such devices on a pair of lines is often referred to as a "line of devices". Typically, many lines of devices can connect back to-a control panel that controls the overall operation of the alarm system.
A typical line of devices, such as a line of smoke detectors, for example, may operate on 36 volts of line power supplied from a power source within or attached to the control panel.
According to certain fire codes, alarm systems, such as those used in commercial establishments, must operate correctly during unintentional losses of AC power. To do so, most commercial alarm systems have battery backup power supplies. These alarm systems may also need to operate only on battery backup power during an emergency, for example, when AC power to the building is intentionally turned off. Typically, codes require alarm systems to be able to operate anywhere from twenty four to ninety hours before battery power is exhausted in a nonalarm condition.
An alarm system described in Takahashi, U.S. Pat. No. 5,151,683, provides intermittent alarm system device operation in order to conserve power when operating on batteries. In Takahashi, the control panel intermittently supplies power to each line of devices in a sequentially repeating order. While power is being applied to a line of devices, each device on that line is individually polled by the control panel for an alarm condition. In response to the poll, each device responds individually with a status message indicating either a normal or an alarm condition at that device. When all devices have been polled and have responded with a normal status, the application of power to the line of devices is terminated. The control panel then repeats the process with the next line of devices or with the same line after a short time interval has passed. In this manner, power is applied to the devices only when needed in order to check for an alarm condition at that device location. Thus, Takahashi conserves power by applying power to devices only when needed.