Definition of Hookswitch Bypass

In the days of electro-mechanical telephone instruments, the hookswitch was identified as on and off switch for most operations of a telephone. The hookswitch consisted of seven metallic leaves, a notched fiber board, spring and an insulated base which was, as one unit semi-permanently mounted with rivets to the base of the telephone instrument. Eavesdroppers could easily modify the hookswitch so that it could pass audio from the handset down the telephone line even though the handset was setting on the instrument’s cradle. This type of eavesdropping was referred to as a

Hookswitch Bypass.

In the early 1980’s, most manufacturers of electronic telephone instruments decided that the cost, simplicity, and ease of installation of the printed circuit board would make a micro-switch ideally suited to be used as a hookswitch. The use of the circuit board hook switches created different eavesdropping attack challenges. However, the bottom line is that regardless of whether the telephone instrument is electro-mechanical or electronic, the Hookswitch Bypass is still one of the favorite forms of eavesdropping by professional eavesdroppers. The Hookswitch Bypass attack most always captures both room audio when the phone is on-hook, and both sides of the telephone conversation.

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For a complete glossary of terms relevant to Hookswitch Bypass please click here