aka get a flip phone.
If you really need to be sure, you can also hire a professional and they will verify that for you, too. Try to do that with iPhone software and hardware.
Every flip phone since 1997 has had apps.
Internet
Sure they do. I used to develop web sites for flip phones.
or sensors
Well, isn't that the point of a flip phone these days? That you don't want to be constantly sensed, tracked, and tabulated? Sounds like a feature, not a bug.
Also, they don't have kill switches
There's no better kill switch than the ability to pop out the battery.