The company supplies a response system. Personal Emergency Response System (PERS) is an electronic device designed to let a patient (often disabled or older person) summon help in an emergency. A PERS has three components: a small radio transmitter (a help button carried or worn by the user); a console connected to the user's telephone; and an emergency response center that monitors calls. When emergency help (medical, fire, or police) is needed, the PERS user presses the transmitter's help button. It sends a radio signal to the console. The console automatically dials one or more pre-selected emergency telephone numbers. Most systems can dial out even if the phone is in use or off the hook. (This is called "seizing the line.") Most PERS are programmed to telephone an emergency response center where the caller is identified. The center will try to determine the nature of the emergency. Center staff also may review medical history and check to see who should be notified. If the center cannot contact the patient or determine whether an emergency exists, it will alert emergency service providers to go to the home. With most systems, the center will monitor the situation until the crisis is resolved.