MD-2105R is wireless smoke detector, it adopts thermistor sensor and photoelectric infrared LED indication, tamper switch button, built-in buzzer, exact detect smog density when it over the standard level (UI 217 / 3.2%/feet), it can make the alarm by itself via built-in buzzer, and also send out the wireless alarm signal to alarm control panel at the same time, low battery indication that make once sound in each 2 hours via built-in buzzer, easy to install on ceiling or wall using the screws with countersink heads which had packed in the package.