dial tone is dial tone. What you are getting is the occasional moment when the internet goes down for any reason. like when a tech pulls a reverse pad or kills a system for a moment. The alarm system is desighned to notify upon loss of dialtone as soon as it returns. Some even respond via an fm output antenna to notify the police dept. Word of caution, If you see asighn that there may be an alarm system, tell the subscriber right away to call his alarm company. I think you could be held liable for any false alarms.
This is CABL.com posting #142782. Tiny Link: cabl.co/mLi6