Retrofit switch activated headset lifter

Telephone sets can be fitted with auxiliary headset features but they will still require mechanical lifters to raise and lower the handset in response to a call. The lifter needs to be in circuit with some portion of the telephone set but it is impractical to modify an unlimited number of disparate set types. To solve this problem, the audio line cord, which is easily detachable, is passed through the lifter system and manually operable remote switch. The switch issues signals in tandem with audio signals on the handset cord and the lifter system differentiates the signals to respond only to switching signals intended to lift or lower the handset from its cradle.