You moved into a place with a pre-existing security system
Sometimes when you buy a home, a home security system is already in use. All the devices work, are hung in the right places, and are ready to go. In this instance, you might find that you have to call and start a new contract. A Vivint expert will still show up to make sure there are no compatibility issues, and they may offer ideas on an upgrade or two. It's a fast appointment, and you can have your 24/7 monitoring set up without worrying about any new alarms and cameras -- unless you add on.
The old owners can give an existing Vivint contract to you for a nominal transfer cost to make the process easier. If the outgoing residents are moving to a condo or retirement community, turning over the security contract may be a part of the sale.
You need to move and bring your old components with you
You might need to bring your existing Vivint system with you to your new home when you move. It should be fairly simple to transfer, as most alarms and smart devices are portable. You can take down each device by yourself or use a professional expert to come and take care of everything. Then a pro will hang the same components -- and any additions you need to put in -- in your new house. And your home security contract will keep the same.