NT502 

        *  Subminiature volume: 81 x 36 x 18.5mm
*  Frequency: 58KHZ or 8.2MHZ for option
*  Alarm Sound: ≥95db±5%.
*  2 or 3 alarm function
*  Standby time over 3 years
*  Normal or Super lock for option
*  Light and Sounds indication for switch on/off
*  Low battery indication

3A