I've run into an issue while doing an integration with a nurse call system, where the nurse call system expects the user to dial a digit to inform the nurse call to disconnect.

When a nurse receives an alert on their wireless IP phone, triggered by a patient call on the nurse call, the nurse has an option to accept the alert, and then to call back into the room and speak to the patient through the audio channel of the nurse call system (via my analog port and the nurse call system's "wireless telephone interface"). If the nurse presses the End button on their phone, the nurse call fails to detect the disconnect, and holds the line open until my analog port returns an off-hook "howler", and then eventually the port disconnects. The only option I have on my system is to send a typical disconnect notification (drop of loop current or battery reversal), but I don't have an option to configure a DTMF digit to be sent prior to disconnect. As mentioned above, the nurse call expects the nurse to dial a specific digit on their phone, prior to hanging up, to trigger the nurse call to disconnect the port.

I have two options: replace the analog "wireless telephone interface", on the nurse call system, with a SIP integration ($$$), or find a Viking Electronics-type device that will detect my drop in loop current or battery reversal and send a pre-programmed DTMF digit to the connected nurse call system. My choice, if something is available, would be to find something to add in between, to do the latter.

I've found devices from Viking Electronics and Sandman that perform functions due to lack of disconnect notification, but so far I've been unable to find something that does exactly this. It seems like something that should exist, maybe for interfacing phone systems with voicemail systems, where the voicemail system is expecting a digit (such as A) that the phone system is unable to send it.

Any help is greatly appreciated.