Lineman's handset

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A lineman's handset, also called a test set or butt set (or a "goat" or a buttinski), is typically a very durable one-piece telephone that integrates an earpiece, a mouthpiece, and a dialing interface (originally a rotary dial, but now more commonly, a 12-button DTMF keypad). It is commonly used by technicians for testing local loop telephone lines in telephone exchanges and outside plant.

In addition to the basic features listed above, some test sets may include:

• speakerphone
• redial
• talk/monitor toggle switch
• mute
• hookflash
• tone/pulse dialing via keypad
• low-pass filtering of data communications (such as DSL)

A removable hook is included for placing the handset on a tool belt. It can be moved to the receiver side, mouthpiece side, or removed altogether based on the technician's preference.

Butt sets typically connect to the telephone system via a pair of alligator clips that can include a piercing spike or a bed of nails to allow connecting to wires without stripping away the insulation. A heat coil adapter can also be used. Lineman's handsets are used for installation and troubleshooting, and can hook into the phone system anywhere the lines are exposed, such as in a phone jack inside a customer's house, in the box where a home's phone wires connect to the telephone company's lines.

Wherever there is an appearance, whether in the exchange or field, a butt set can be used to "butt in" to a telephone circuit using the test leads. The most common way is to clip on with alligator clips to metallic lugs, either on the frame or at a cross box, on the tip and ring side of a phone line. This allows the technician to check for dial tone, ANAC or ringback a number to determine the phone line being worked on, or place a call.

When using a butt set, the technician is always mindful that he is essentially an extension of the customer's home phone. If the talk/monitor toggle is moved from monitor to talk while the customer is on the line, it will sound as if someone else has picked up the phone. Also, a technician can be interrupted by a confused customer, who hears strange voices on the line.

A beige box is a homebuilt version of a lineman's handset.