Duracel LR1 battery, ideal for any type of alarm that requires 1.5v batteries to operate. As a rule if your alarm takes two small batteries it will have a 3v circuit. This goes for the whole range of fox bite alarms and these duracell LR1's are the recommended type.

27mm (L) X 11mm (D), High performance long lasting power

Recommended batteries for the Fox bite alarms