Am I obligated to honor a service contract after a business is sold to another entity?

The answer depends on several factors. One, when you say Company B bought Company A, do you mean that Company B bought the stock/equity of Company A, or just the assets?  If the former, then you are still dealing with Company A, just with different owners and a different name (if you buy 100% of the shares of IBM and change its name to BMI, IBM still exists and its contracts are still in force.)  Unless your contracts allow you to back out if different people own Company A, which I very much doubt, you would still be obligated. Two, assuming that Company B didn't just buy the stock of Company A but rather bought the contract itself, do your contracts provide that the alarm company can assign them?  If you signed the form contracts provided by the alarm company, they probably do.  In the absence of such a provision, most contracts are freely assignable, except those for personal services (e.g. a band can't assign its contract to play at your wedding to another entertainer, but a lender can assign your loan to another person or entity.)  I'm not sure whether alarm monitoring services would be assignable absent a contractual provison allowing it, but I bet there is such a provision in your contracts. Three, have you attempted to cancel the contracts?  Even if the contracts are no longer binding, you would probably be responsible for paying the new alarm company the fair market value (quantum meruit) for the services it has been providing since it took over, although you would not be obligated to keep them on in the future.