These phone sets are professionally made with the highest quality new parts, 100% ready to use right out of the bag and designed to check for continuity and loop check. Made for electricians to work on non-energized single conductor cables and multi conductor cables no matter how long they are. Simply clip one phone on each end of the wire to check. Communicate two people loud and clear, no noise or interference. All sets include heavy duty on/off switch, super bright LED light that lets you know when continuity is complete, 12V 23A INTERNAL battery, Velcro ties to secure wire leads, kink less leads, carrying case, and support on how to use the thru our email or phone support. *WARNING/CAUTION/DANGER: *Do NOT use on LIVE circuits or energized wires of any voltage. Misuse may result in serious injury or death. We are NOT responsible for any misuse that leads to personal injury, property damage, damage to the phones or any other equipment of any kind.