Feature 1.Highly sensitve. 2. Simple and convenient to use, no adjustment is required ; 3. The detecton distance will not be changed when the battery voltage drops from 9V to abou t 7V 4. Low power consumpton ,can work for 40 hours contnuously 5. There is automatc and continious alarm when the battery is used up 6. Switch on /off audio prompt functon 7. With external rechargeable socket hole 8. Has audio, light and vibraton handoff switch