@Ann28786 I don't think there is anything official written as far as Airbnb is concerned, about how long you have to keep someone's left-behind stuff.
Basically, if someone forgets something, that's their responsibility. But of course it's nice to get it back if possible.
Is the guest mad at you? He wants you to pay for them or something?
You know, not everyone is a phone addict 🙂 I don't even use use Airbnb app, I only use my laptop. And sometimes a guest might be travelling where there is no cell signal, or they are busy.
Not everyone uses technology in the same way. Believe it or not, some people don't even use a smart phone at all.