No matter which route you decide to go, as a former public safety dispatcher, I suggest calling your local 911 agency and having them add a "premise history" to your sister's address. Tell them what medical problems your mom has, where a hidden key is if you have one, info on if there are pets in the house especially if they're aggressive, and contact info for you and your sister. Even if you go with one of those systems that is monitored by an alarm company, call the 911 agency - I can't tell you how many times the alarm company DOESN'T have the information available for the responding units even though they're supposed to.