PW-1 module is used for additional calling signaling. It is a circuit mounted inside uniphone, which starts during calling an additional invigilator of any type (most often acoustic or optical) powered with AC 12-24V. In the case of hard of hearing people, the PW-1 module can switch on any acoustic invigilator, for example, one used in alarm systems. In case of the deaf, the PW-1 module can signal calling switching on the light. .