You’re buying a home with home security alarms
A new house may come with an existing home security system. All the alarms and cameras work, are hung in the best areas, and are ready to go. In this instance, just get the phone to call and start a new contract. A Vivint professional will still show up to make sure there are no usability issues, and they may offer options on where you should replace bad outdated components. It's a preliminary trip, and you can have your alarm monitoring set up without worrying about any new alarms and cameras -- unless you add on.
The previous homeowners can give an existing Vivint contract to your family for a small transfer fee to make the process easier. If the owners downsize to an apartment or smaller home, you keeping the Vivint service may be an addendum of the sale.
You need to move and bring your existing components with you
You may want to take your existing Vivint system with you to your new house when you move. It should be fairly easy to transfer, as many smart devices are plug and play. You can remove each component by yourself or use a Vivint installer to take care of your devices. Then a pro will put in the same components -- and any smart services you need to add -- in the new place. And your home security contract will stay the same.