Hi,
i've written a simple plugin for Nagios to monitor SER. It leverages sipsak to register and "ping" a contact on a SIP server (tested with SER).
Please find the plugin below, consider it GPL2-licensed (read: if you improve it, i want you to let me know ;) and without any warranty. We never used it to wake up an engineer, but we've been using it for a few weeks on our test monitoring instance.
err, not to forger: consider it alpha level software.
share & enjoy.
-- axelm