Timer which fits onto telephone handset - indicates duration and cost of call and includes buzzer operating one minute before end of call

摘要

The timer, for telephone handsets, is mounted directly onto the handset and measures the duration of a telephone conversation and hence the cost. The timer is set manually to the wanted duration of the call by the user after dialling his number and emits a buzzing sound typically 1 minute before the set time elapses. This buzz can be heard by both parties to the conversation. The timer typically has a maximum operation time of about 30 minutes.