You moved into a house with a pre-existing home security system
Sometimes when you purchase a house, a security system is already in use. All the components work, are placed in the right spaces, and are ready to go. In this case, you might find that you have to call and establish a new service contract. A Vivint installer will still come to your home to ensure there are no usability problems, and they might offer ideas on upgrades. It's a quick trip, and you can get your monitoring set up without having a bill for any new components -- unless you make additions.
The previous homeowners can move an existing Vivint contract to your family for a small set-up fee to make your life simpler. If the outgoing residents are moving to an apartment or retirement community, you keeping the security contract might be a condition of the sale.
You are looking to move and take your old devices with you
You may need to take your existing smart devices with you to your new home when you move. It should be pretty easy to do, as modern smart devices are wireless. You can take down each alarm or camera by yourself or contact a professional installer to come and dismantle the system. Then an expert will hang the same features -- and any additions you want to have -- in your new house. Your home security contract will stay the same.