Where does it come from?

In recent days, I can hear a sound, something like a beep sound. It is short, but is repeated at intervals. I thought that battery of a smoke alarm or a carbon monoxide alarm has run out and I checked them, but they were no problem. It comes from somewhere. Perhaps one of these batteries 'in the next door' has run out. The problem is that it's a vacant house for a while. A family moved out, and new residents haven't come yet.