The Model 420 Buzz Box was developed to aid Signalmen in ringing out or point checking wiring in signal cases and bungalows.  Compact, light-weight.  With Harness Accessory, can be worn around the neck to allow the Buzz Box to stay with you, safely, as you work.  Will not buzz through signal battery, either polarity (8 volts DC – up) or through relays with DC coil resistance of 100 ohms or greater. Up to a nominal 17 volts, circuit design prevents battery buzz-through.  From approximately 17 volts-on, the thermal breaker prevents buzz-through.  If the thermal breaker activates, a short wait period will be necessary before the Buzz Box is ready to resume operation.  Further note:  sustained  exposure to over-voltage (18VDC – up) may result in damage to the Buzz Box.  Operates on a standard 9 volt battery. Lithium battery furnished.  Battery can be changed in a few seconds without disassembly.  Accessory Neck Harness and Carry Case are available in Kits and separately, per below.