In the course of my work, I often need some kind of timer (a stopwatch or a countdown timer, depending on the situation) for my experiments. I bought a photographic timer from Jessops, mainly because it had nice big displays and could run three different countdown intervals at the same time, which is often useful for me. However, the big problem is the noise. It beeps when you press buttons to set things and it beeps continuously when the countdown period expires. Loudly. That's obviously what you want in a darkroom, but its not what you want when you're working with animals.
So I'm looking around for a flexible timer with a vibration alarm that can handle a stopwatch or multiple countdown intervals. I remembered talk on various GTD mailing lists and blogs about the Invisible Clock, which seems to do all that and more. I'm thinking about buying one, but it's quite a lot more expensive that other timers, and I'm wondering if it's worth it. Does anyone have any experience of it? Is it worth the money? It would also come in useful for giving talks and lectures, because you can set it for the length of your talk and it buzzes you half way through, five minutes before the end and then when you've got to shut up because you'll be hooked off the stage with one of those comedy giant shepherd's crooks.