You've gone to all the trouble of getting new up to date Standard Form Agreements and getting your subscribers to sign them.  Can you change the terms of your agreement by sending out an email to your subscribers?  That might alleviate the need to get new updated form agreements or getting your subscribers to sign new updated agreements.  After all, we all get those obnoxious notices from the credit card companies and banks letting us know that they've changed the terms of their agreement with us.  No need to confirm or respond, we're stuck with the new terms.  Whatever, we don't bother reading them.
    But what's good for the credit card companies and banks, and perhaps other industries, isn't going to work for you.  You can't change the terms of the alarm contract without getting assent from your subscriber.  And unlike the credit cards and your bank accounts, continued use of the alarm system is not going to be sufficient confirmation of assent of new terms.
    In the alarm industry we rely heavily on "protective" provisions in the alarm contract.  These provisions are very carefully worded and sometimes they need to be changed to keep pace with changing law.   That is not the kind of change you can make unilaterally with your subscriber without getting a new contract or modification of the existing contract signed.  In fact I wouldn't be comfortable changing any term of the agreement that had any significance at all by unilateral email or other notice.  Since most of the terms in the alarm contract are artfully drafted there isn't much that you can change by sending an email or letter.  Sure, you can change the times you'll provide service, from 9 to 5 to 10 to 4, your phone number, maybe a few other things that perspectively benefit the subscriber, like raising the limitation of liability clause, but any important enough for you to want to change isn't going to be able to be done unilaterally.
    We are also familiar with changing Rules and Regulations.  If you have an office lease it probably contains a provision that you agree to the landlord's rules and regulations which can be modified from time to time.  That doesn't mean the landlord can raise your rent, your insurance requirements, reduce your space or shorten or add to your lease term or the amount of rent.  
    So the best way to conclude is this

  • regularly visit your subscribers to suggest upgrades to their equipment and services
  • regularly upgrade your Standard Form Agreements
  • regularly have your subscriber sign new Agreements rather than rely on automatic renewal
  • don't look for shortcuts or out of the box schemes; they don't work.  Stick with the RMR model.