Portable Hand Held Metal Security Detector With Free Battery

Highly sensitive 
2) Simple and convenient to use, no adjustment is required; 
3) The detection distance will not be changed when the battery voltage drops from 9V to about 7V; 
4) Low power consumption, can work for 40 hours continysly; 
5) There is automatic and continues alarm when the battery is used up; 
6) Switch on / off audio prompt function;