Somebody's pre-emptive proximity alert[1] has been going off behind my house for the past few hours. Loud, high-pitched, and AFAIK, it can't be turned off except for a timed sleep-mode or the presence of a predator overhead. I don't know enough to identify the make and model[2] from the sound, but I'm pretty sure that's what I'm hearing. I expect to be hearing it every day until autumn.
[1] Rather than sounding when a potential malefactor gets too close, it continuously sounds a warning that the area is defended and others are not to approach, regardless of the presence or absence of anybody to be warned off.
[2] Er, I mean genus and species. But I'm fairly certain it's one of the pocket-sized models, or at most one size up.