You moved into a home with a pre-installed security system
Sometimes when you purchase a home, a modern security system is already in use. All the components work, are placed in the right places, and are ready to go. In this case, you might discover that you have to call and establish a new monitoring contract. A Vivint professional will still show up to make sure there are no usability problems, and they might offer ideas on where you should replace bad outdated components. It's a preliminary appointment, and you can get your 24/7 monitoring set up without having a bill for any new components -- unless you make additions.
The previous owners can transfer an existing Vivint contract to your family for a small transfer cost to make the process easier. If the previous owners downsize to a condo or smaller home, you keeping the security service may be a condition of the sale.
You need to move and bring your old components with you
You may want to bring your existing home security components with you to your new house when you move. It should be pretty simple to transfer, as most components are portable. You can remove each alarm or camera yourself or contact a professional installer to come and take care of your devices. Then a pro will hang the same features -- and any additions you want to make -- in your new home. Your home security contract will keep the same.