Such an annoying noise when it happens, but necessary. At least you found the culprit and have now disarmed it.
I remember the first time it happened to me it was 32 years ago, not long after my mother died. I kept hearing this beep and had no idea where it was coming from. (at that time we hadn't had a smoke alarm very long and I had no idea that they did this when the battery was low) I got into a real state about this beep because no matter which room I was in, the beep was always somewhere else, the alarm was on the landing ceiling. As I said, it wasn't long after my mother had died and as she had always said that she would come back and haunt me, I was getting very freaked out by it.

Betty x

Jan the way the new ones work does not sound like the best idea exactly for the reasons you pointed out, you know what they say, "if it ain't broke, don't fix it"