Fire and security panels transmit audio over phone lines, just like fax machines do. However, VoIP can be a little too unstable for them to communicate with 100% reliability.
The solution is to call your Fire/Security company and have them change the communications protocol of the panel to SIA. Tell them to send out a technician and re-program the panel to use SIA.
"SIA" is one of several communications protocols (basically like programming languages, but with sound), and is known to work very reliably with security and fire panels. Most panels communicate with the "ContactID" protocol, which isn't reliable over VoIP.