Or at a minimum know where/what your modem is. Unplug that bad boy and all your IOT stuff goes back ot being things, not of the internet.
There are only two viable choices:
1) Logout and/or factory reset all devices. 2) Delete the online accounts associated with all devices.
I recommend both, as otherwise there are edge cases where unsafety could remain.
Disclaimer: I did #2 when I left a long-term partner (along with a complete list of all credentials that needed to be rotated or disabled), both to be able to provide her absolute certainty that I could not somehow spy on her consummating her affair, and to ensure that I could not be placed into legal jeopardy by either of them as punishment for knowing that he existed at all. There is a serious legal risk if you retain access after moveout. Do not permit that risk to impact you.
Without an internet connection, they can still be controlled by a client that is on the same LAN as the bridge.
EDIT: Oh, yes, you’re right about the “it’s not Bluetooth” nitpick, for whatever good that is to this conversation :)
I maintain a version of your "complete list of credentials" professionally - and every time I've left a job I've supplied that list saying: "Here are the company-related credentials to which I've had access. This list is best-effort and may not be complete. Please respond acknowledging I've advised you to change these and any other credentials I've ever had access to."
At least being on equal footing with everyone in the household so it's not seen as an avenue of control (which most domestic abuse scenarios are all about) would be a great first step.
In a few states I'm aware of, if you commit any form of domestic abuse and deprive the victim access to a phone, it's a separate charge. It can't/doesn't stop it from happening but it disincentivizes it by making the punishment worse.
I suspect a lot of this IoT nonsense will eventually attract the same riders. A documented history of remotely tampering with locks or lights, blasting heat in the summer and blaring music at full volume in any context will eventually become factors in a case of abuse.
Source: spent my entire childhood in a domestic abuse and domestic violence situation.
Also abusers often work very hard to make it difficult for the abused to leave: make them quit their job, cut off their outside social ties, make them pregnant against their will, etc.