A smoke detector

A smoke detector is an inexpensive device that saves people from being killed in a fire.
The device is triggered by smoke: it begins to emit a very loud beep. The detector is designed to Wake up sleeping people, or draw the attention of neighbors to what is happening. According to statistics, the presence of such a device reduces the number of deaths in fires by 75%, as evidenced by the experience of other countries, where the installation of a detector has long been mandatory.