I use a vibrating alarm clock. It's a regular alarm with a wire going to a bed shaker (a 3/4" high disk with a vibrating mechanism inside - much like the ones in game controllers). The shaker is located between the mattress and box spring under my head.
Sometimes it startles me awake, which is an unpleasant feeling, but it works for me all the time. And, given that we have a foam mattress, the buzzing is absorbed enough for my wife to easily sleep through it.
I recently discovered Bellman & Symfon, a Swedish company that has some very attractive (naturally) products. Their vibratating/flashing alarm clocks integrate with wireless smoke detectors. I can easily get a stand-alone strobed smoke detector in just my bedroom, but that doesn't help if the other end of the apartment is in flames. http://www.bellman.com/en/our-solutions/fire-safety-solution...
Sometimes it startles me awake, which is an unpleasant feeling, but it works for me all the time. And, given that we have a foam mattress, the buzzing is absorbed enough for my wife to easily sleep through it.