In the Netbell system, you can ring the bells/buzzers manually for emergency with a push button switch connecting to the digital input. Here are the models with digital inputs: Netbell-2, Netbell-K, Netbell-K-M2, Netbell-KB, Netbell-KB-M2, Netbell-KL, Netbell-KL-M2, Netbell-4K and Netbell-NTG. 

This push switch is pre-wired on 10ft cable, you only need to connect to one of the digital inputs terminal, and configure the software to trigger the bell(s). It will ring the bell(s) once the button is pushed, and stop once it's released.

Please leave a note for us when you purchase this item, that which Netbell device you have, so that we will know what kind of cable we need to supply with your order. As the Netbell-2 uses different cable for the input connector.