I am completely deaf in one ear, and can sleep for hours through a normal alarm clock if my good ear is in the pillow. This clock has a small 5″ disc attachment that slips under your pillow between the bottom sheet and the mattress and vibrates you awake (I think some people put it between the mattress and the box spring if they find the vibration too intense). The sheet holds the disc pretty securely — I’ve never noticed the disc moving around at all. I suppose if you sleep with a really thin pillow you might feel the disc, but I don’t feel it with a normal pillow. You could probably also put the disc at the foot of the bed if need be.
You can’t change the nature of the vibrations, though there is a setting for a variable pitch/loudness tone alarm (you can use the tone and the vibration together or separately). I’ve never used the tone setting. The vibrations are enough that I instantly wake up when it goes off (at least enough to hit the snooze button!), although my husband says it doesn’t wake him up. But I also don’t let it go on and on for 10 minutes, and my husband is a deep sleeper.
For those of us who are hard of hearing, this alarm clock actually works. As I said, I can’t fully trust any sound-based alarm, and I was looking for something that would reliably wake me up, but let my husband and kids continue sleeping as needed. This works beautifully.
The model I have is the SBD375ss, which has a dual alarm. They also make a few models without the dual alarm that are about $10 cheaper. I find the dual alarm very useful because I have two different wake up times (5am or 6:30am) depending on the day of the week. And, honestly, resetting the time day-to-day can be a pain because there’s no reverse feature for setting time with the clock. If it’s set for 6:30am and I need to get up at 5am the next day, I’d have to fast-forward through 22.5 hours to get there. For me, the dual alarm solves that problem. I also recently purchased the travel/portable version of this clock, but haven’t used it yet.