So I set myself to the task of going shopping [UGGGGGGGHHH!] for a timer that I could hear. I read labels and labels and more labels. I finally found a timer at Linens & Things that had an "extra loud" alarm and would "turn itself off after 2 minutes to preserve the battery." When I got it home and tried it out, the beep was even quieter than the one on the stove and lasted for all of ten whoppin' seconds. (I still am entirely clueless as to WHAT turns off after 2 minutes to preserve the battery. Because it sure ain't the alarm-noise.) I was pleased with the the store and thankful for their cheerful refund of my money.
So I internet-searched. I found an "extra extra loud" timer. I bought it and it arrived today. It's still not quite what I want, but it's good enough. I wish it were louder, but it's a darn sight louder than any other timer I've run across in recent years. And while I was testing the new toy, Philip could hear it while he was vacuuming in the next room. That says something about the volume!
The alarm buzzes for a full 60 seconds. Wooo hooo! Long enough that there's still something buzzing even if you missed the start of the beep. Another nice feature is that it doesn't just turn off and beep when the time runs out. Instead, it starts counting up so that you know how long ago the timer ran out; that'll help too! If you miss the alarm, it's nice to know whether you missed it by 3 seconds or by 5 minutes.