DT Systems Micro-iDT Plus Add-On / Replacement Collar: * Maxx-Range internal collar antenna system * Can replace any lost or damaged Micro-iDT Z series collar unit with a serial number that starts with a letter * Fits small to large dogs * Rechargeable * Waterproof * Digital technology * 900 yd (1/2 mi) range * Positive vibration * 16 levels of intensity adjusted from transmitter * Built-in magnetic on/off system