DT Add On Collar Micro - This collar is compatible with any Micro-iDT PLUS system, and it can also replace any lost or damaged Micro-iDT Z series collar unit with a serial number that starts with a letter (ex. #A12345). Digital TechnologyAdds to the Micro-iDT PLUS training systemReplaces any lost or damaged Micro-iDT Z or PLUS series training system (only for systems with serial numbers that start with a letter)Up to 900 yard (1/2 mile) rangeLightweight and waterMAXX-Range Internal Antenna SystemRechargeable Ni-MH batteriesBuilt-in safety shut off system