Definition. “Unit of service” means any of the following: Purchase and installation; Maintenance or repair; or Monthly cost of a covered system or rented device or equipment. A personal emergency response system is an electronic device or system which enables a participant to secure help in an emergency and may include: A device connected to the participant's telephone or other device and programmed to signal, upon activation of a help button, a response center with properly trained staff on duty 24 hours a day, 7 days a week; A portable help button to allow for the participant's mobility; and A motion detector when necessary for the participant's health, safety, and welfare.