The HD2 has two clearly defined buttons, nursecall button & light control button. The light button provides a momentary closing contact which can be used to trigger an external device such as our Intercall LCU to switch lights on and off. In order to operate the HD2 the call points jack socket requires a stereo jack socket modification. L622HL, L722HL, L753HL, L762HL & SCP/HL all have the suitable stereo fittings.