... Circle design of the detecting part, extended the detecting area;3. Low-power design, USB charger;4. Audio & Visual alarm ... Parameter:1. Power Supply: standard 2*AAA battery, or rechargeable battery;2 Power: 270 mW;3 Working frequency: 22kHz;4 Working current: ... for security check;2 Custom, police, border, security, government department;3 Bank, hotel, KTV, club, entertainment place;4 Medical & food ...