Flashing Strobe Prism in Canister is totally selfcontained. All electronics and power supply housed within prism canister. Designed to be used in all offsets holders from other manufacturers must be compatible with M20 thread type. Ideal uses, adverse weather conditions, tunneling, mining, and night survey, and for use in locating gear. Battery life under normal conditions 7 days (24 hours). Flashing Strobe Prism in Canister or with target. Prism is 2.5" dim.