Sold house and left SimpliSafe system for new owner

I believe when the new owners take ownership (and sign up for and activate their own account), the base station serial number automatically goes to the new name/address on the account (because they own the base station now, they have to sign up for their own account associated with that base).  In the meantime, just keep an eye on your account to make sure you're not being charged for monitoring if you had a monitoring plan, in other words, make sure it was cancelled properly for that base station serial number/account.

@terrylittledad I would take a page out of my ADT playbook.  When I was a "departing" ADT customer, everything was in writing after I called them.  Email, fax and certified letter, return receipt were all employed due to the fact I didn't trust ADT as far as I could throw them, and it turned out to be a very prudent move.  (You can use a google site search if you care about my long saga though I doubt it. :-)

I would send at least an email to SS to confirm your instructions.  Note that SS doesn't delete any records, only deactivates them, and I have personally found this to cause a few issues over the years.  Once you confirm your instructions in writing, move on and enjoy your new home.  Live long and prosper.