Things like RING doorbells and security cameras, kitchen appliances, furnace and AC thermostats, garage door openers, home sound systems, etc? So many things are now connected to the internet in some way.

Do sellers leave all the devices when they leave? How does the buyer ensure the previous owner has thoroughly deleted access? What about liability for the seller with perhaps claims of violating the new owner's privacy?

When I bought my house just over 2 years ago, the seller had a small security camera system installed.
There was 2 cameras and a DVR.
The seller did a complete factory reset on these devices and left them with the house.
I ended up not using them as I wanted a more comprehensive camera system.

There's also a "smart" thermostat that has an app for your phone where you can control the temperature.
I suppose it's possible that the seller may still have the app installed and could monkey with our temperatures lol.
But we've never seen anything like that happen.

A factory reset was NOT done on the thermostat (likely cuz the interface is SUPER unfriendly)

The devices are not so expensive, installation more expensive. I would offer the buyer to keep the hardware, reset it to factory. If not wanted, I would not lower the selling price as would have to pay to have them removed.

You can factory reset all of it and enter your wifi info and passwords , if the ring camera and thermostat along with any other security alarms were left behind. I personally if selling my house with any of that left would do a factory reset before turning it over to the new owners.

Issues like that should be clearly stated on the sellers disclosure form. Otherwise a good Realtor should state who owns them in the offer and contract.
State law may be different where you live.

I like WiFi connected devices. Kind of a hobby. I have lots of Zwave lights and sensors, appliances that connect to SmartThings, connected tvs, garage door openers, exterior led lighting, a connected car, 6 cameras, Nest thermostats and more. Easy to connect and monitor while we travel.

My wife is a real estate agent.

Typical procedure is that anything affixed to the property is presumed to come with the property, unless otherwise mentioned. Appliances do not come with the property unless affixed (built in fridge, built in cooktop, built in range vent, water softener, Uber counter water filter, etc) or specifically mentioned (washer/dryer).

Smart devices that get left should be factory reset (as a safety practice for the seller, clearing the device of personal information). As the buyer or new tenant, you have physical access to the device and can factory reset at your convenience when you take possession.

As the real estate agent, we often set that stuff up for our tenants when they move in. Usually a few days after the client closes on the property, we schedule a day to drop by to drop off gifts, set up smart devices, program thermostats, and fix any small problems that are left unresolved from the home inspection (self closing garage door hinges are a frequent one). Then we go out for dinner.

We sold our house last year. Everything went with the house. Stove, fridge, dishwasher, washer, dryer, Ring doorbell and all Ring cameras, Nest thermostat, garage door opener, etc.

Thanks for all the replies.

I plan to put them all on a new Gmail address with a new password.

Remove them from my connected Amazon account.

Give them the Gmail and password and wish them luck.