You moved into a home with an existing home security system
Sometimes when you purchase a home, a security system is already in use. All the devices work, are installed in the best places, and are ready to go. In this case, you might discover that you have to call and start a new monitoring contract. A Vivint professional will still show up to ensure there are no integration issues, and they might offer suggestions on where you should replace bad outdated components. It's a preliminary trip, and you can have your 24/7 monitoring set up without paying for any new alarms and cameras -- unless you make additions.
The outgoing homeowners can transfer an existing Vivint contract to your family for a one-time set-up cost to make the process simpler. If the outgoing residents downsize to an apartment or retirement community, you keeping the home security service might be an addendum of the sale.
You are looking to move and take your existing components with you
You may want to bring along your existing smart devices with you to a new house when you move. It should be pretty easy to accomplish, as most alarms and smart devices are wireless. You can uninstall each component by yourself or call a professional installer to come and take care of everything. Then a pro will hang the same features -- and any additions you want to have -- in your new place. And your home security contract will stay the same.