It usually beeps like that because the battety is dying... Just change the battery!

Nowadays in the US, where it looks like this was taken (why do I feel like I have to add that anytime I mention the US lest 50 people point out that not everything revolves around the US), that could get you shot blindly through a door as your neighbour satisfies their blood lust to finally kill someone with one of the many firearms they keep for innocent passerby they think they can get away with saying made them fear for their lives.

It's possible they tried and can't find the damn thing. That chirp is just infrequent enough to make locating the source difficult.

Yeah hell no to a month of that nonsense. I give it one day before I'm jumping a fence and smashing it with a hammer.

After a week i would have stolen it and tossed it.

1 year. Our neighbor has been doing this for a year.

The building to the right of the sign looks like it may be a multi-unit dwelling, so it may not be clear who the culprit is. Also, many people don't know their neighbors very well, or may have anxiety or some type of fear of social situations. In this case, they may be concerned that it may turn into a confrontation, especially if they let this go on for a month (as others have said, three minutes is my max tolerance for this). And the sign is funny and not particularly aggressive, although it may not be effective on the type of person who 1. throws their smoke detector outside instead of replacing the battery, and 2. allows it to continue beeping for a month. Maybe the OOP felt a little public shaming is in order.

Not next door to me, but a house on my walk has done this twice over the past few years. It's been going on for at least a month this time, every time I walk past BEEP BEEP BEEP! I think the house is a rental. If I lived next door to that, I would 100% break in and solve the problem.

nah wind chimes are nice

Allow me to introduce the 9mm handgun.