I think the ideal thing to have done would've been to either:
1. Take it with me, maybe charge it up and wait for the owner to ring it and then make plans for them to collect it. I didn't do this, partly because:
- I thought the person would miss it quickly and come back for it by retracing their steps, didn't want to make that impossible for them
- I don't live close to where it was lost so collection would be a pain
- I spend enough time trying to organise collection of my *own* stuff through Freegle, Gumtree etc and you know from the #FreegleWoes hashtag how that usually goes
2. Leave it on the wall as I did but put it in a clear plastic bag to protect it from rain. I only had an opaque bag which would've hidden it from the person searching for it.