You moved into a house with a pre-installed security system
Sometimes when you purchase a house, a security system is already installed. All the alarms and cameras function well, are installed in the correct spaces, and are ready to go. In this case, you might find that you have to call and set up a new monitoring contract. A Vivint expert will still show up to ensure there are no usability problems, and they might offer options on upgrades. It's a fast visit, and you can have your alarm monitoring set up without paying for any new alarms and cameras -- unless you get some new devices.
The old homeowners can transfer an existing Vivint contract to you for a nominal set-up cost to make the process simpler. If the owners are downsizing to an apartment or retirement community, turning over the security contract may be a part of the sale.
You need to move and take your existing components with you
You might want to bring your favorite home security components with you to your new house when you move. Luckily, it's fairly easy to transfer, as many alarms and smart devices are portable. You can uninstall each component by yourself or use a Vivint expert to take care of the system. Then a pro will hang the same devices -- and any additions you need to put in -- in your new place. The home security contract will remain the same.