SportDOG FieldSentinel 1/2 Mile Electronic Training Collar - The SportDOG FieldSentinel, with BodyGuard Health Alert, keeps your dog safe even when out of sight. It is the world's first remote trainer with health alert technology. SportDOG's proprietary technology alerts to potential health concerns via tone, vibration and LED on the handheld device. It's like a check engine light for your dog! 7 instantly selectable static stimulation levels; lowithmedium/high ranges Vibration and tone options Bodyguard health alert technology Waterproof to 3 ft 24-hour battery life with rechargeable Li-Ion batteries Transmitter battery lasts 40-60 hours per charge. Receiver battery lasts 140-160 hours per charge. Expands to 2 dogs with purchase of Add-A-Dog collar Fits dogs 8lbs or larger