DTMF code from the outside

I have a fully functional FreePBX distro setup with a few Cisco SPA303 phones at an office, plus an exterior CyberData intercom which is connected to a door striker. When a visitor hits the intercom, it rings at certain ring group, and then they can hit a code which releases the door strike and opens the door.

I’m trying to enable this functionality from the outside – is it possible a visitor, say during after-hours, to call the PBX and then enter a certain code which will trigger the door striker through the intercom (DTMF)?

You just have to provide a way for the visitor to call the intercom. Possibilities include a dedicated DID (not very secure as anyone who knew the number could let himself in), a hidden IVR option, DISA, etc.

The intercom could be set to auto-answer, or the visitor would press the Call button when it started to ring. Once the call is established, the visitor would press a DTMF key to operate the strike.

A frequent visitor could set up a contact on his mobile with appropriate pauses, to automate the entry process.