Well, I just found out one of my dog's triggers.

One of the smoke detectors needed a new battery and started beeping. It's that high pitched beep that's a shortened version of the sound when it goes off for real. I was busy, so I closed the door on the room briefly until I could finish what I was doing and go get the new battery from downstairs.

My husband yelled up to me "Come here! Something's wrong with Radar!" I bolted downstairs and he pointed out how the dog's head was shaking. I touched him and it wasn't just his head - his whole body was rigid and trembling. For a second, I thought he was seizing. He was conscious and aware (so not a grand mal, anyway), so I held him and started soothing him, petting and cooing. He calmed a little, but was still tense and kept staring at the stairs. It was time for dinner, so DH tried to feed him - nope, not interested. He kept going to the bottom of the stairs and staring up.

I went up with the battery and opened the door, so it got louder. Apparently, that very much upset him. Even after I stopped the noise, he was freaked out. I came down again and sat with him; he stayed pressed up against me and wouldn't even consider eating. Eventually, he slept and woke up hungry and now everything is back to normal.

Now, we do have a little more history on him than you usually get from a rescue, but we don't know how much is believable. He originally belonged to an elderly person who died. Their adult offspring tried to keep him briefly, but apparently weren't dog people - they told the rescue that he was unhousebreakable. (This is one of the most housebroken dogs I've ever had.) He also had no medical care for long enough to be wayyy too skinny, not neutered, major dental issues, and had never had a major heart murmur diagnosed, let alone treated. These conditions had been developing for longer than the offspring had him, so I suspect the original owner was too poor to afford good food or any medical care for him. Certainly, the offspring didn't bother. (We did all his medical care as if he'd never had any, including starting vaccinations from the beginning.)

He has some issues, but he's never had anything like this. Something about that sound scares the crap out of him.