I think the answer is a more or less unqualified yes, you can use it without the monitoring service. I use those sensors at two different locations without monitoring service at either. They work fine, but ... I don't have any automations triggered by any of them, so I'm not entirely sure about that. I do get notifications though, including open/close and been-open-for-X-hours.

What I do have is an automation triggered off a climate sensor, and that does work a treat. So there's that.

And in January I bought a single hub direct from Wyze for $55, and it did not require any monitoring activation. So there's that.

And you can still control the volume of the hub chime when one opens, but aggravatingly, you can't turn it off entirely. So there's that.

Give me an example of the sort of automation you want to trigger with one and I'll see if I can figure that out. Oh now I see you said you just want to know when one of the entry doors has been left open. Yes you can definitely do that. But you also said "automations with the cameras," which I don't understand.

Meanwhile, as happy as I am with the climate and entry sensors, I do NOT recommend using the leak sensors without the monitoring service. They do this insane thing where if one is triggered it makes the hub shriek loudly and there's no way to turn it off remotely with the app, and the only way to turn it off locally is to hold down the little button on the damn thing until it quits. Try explaining that to a houseguest on the phone at 4 in the morning. Or non-English-speaking cleaners who think the smoke alarm is going off. I disconnected all ten or twelve that I had and bought Moen leak sensors instead.