Motion sensors with alert

Alert

— this feature means that the sensor is capable of sounding its own alarm, usually by means of a built-in siren.

Such a signal can be very useful in some situations. For example, a siren from a security motion or breakage sensor can attract the attention of witnesses or even the police, significantly complicating the task of an attacker; and the sound from a smoke or gas sensor alerts all people nearby, allowing you to take action to counter an emergency as quickly as possible. Another useful feature of this function is that many sensors with a siren are able to at least partially perform their task even if communication with the control panel is completely lost.