Some cities and insurance companies insist on having alarm systems certified by an outside agency to ensure they were installed properly. Every six to twelve months, you should execute a maintenance check on the alarm system to make sure that all of its moving parts, sensors, and power supply units are still in good working order. For this to be done in the past, an alarm service engineer would have to be physically present. By connecting to the alerted property over the Internet or a radio route and using a compatible IP/radio transmitting equipment, the central station can now do some checks remotely (at the alarmed premises).