Digital Voice: Stand-alone caller ID flashes once every thirty minutes

[AtomicRooster]

Has anyone else noticed this?   A puzzling but minor annoyance.

I moved to digital voice with no issues at all, but we have noticed that every 30 minutes (without exception) our stand-alone caller ID box flashes its screen once, and there is not an incoming call.  We just wonder what this signifies? Is the central office "touching base" with our digital voice system?  I have set up the new voice mailbox and there are not any messages on it (which in previous landline incarnations may have been such a signal).

[prisaz]

I have wireless phones that do the same thing. Light up and say incoming call with no other information, when there is no call. No idea, unless it is some type of  message waiting indicator. I have never looked into it, but it would be interesting to know. NSA open line to see if anyone is talking? Patriot act?