You moved into a house with a pre-installed security system
Sometimes when you buy a house, a modern security system is already established. All the components work, are placed in the correct areas, and are ready to go. In this example, you might discover that you have to call and set up a new service contract. A Vivint expert will still come out to make sure there are no usability issues, and they may offer options on an upgrade or two. It's a fast visit, and you can get your 24/7 monitoring set up without having a bill for any new components -- unless you add on.
The old owners can give an existing Vivint contract to your family for a nominal transfer cost to make the process easier. If the previous owners downsize to an apartment or smaller home, you keeping the home security service might be a condition of the sale.
You need to move and take your old equipment with you
You might need to bring your favorite home security components with you to a new home when you move. Luckily, it's pretty simple to do, as many smart devices are wireless. You can take down each device yourself or call a Vivint expert to come and take care of your devices. Then an expert will set up the same devices -- and any additions you want to have -- in your new house. And your home security contract will stay the same.