I've had a history of sleeping through alarm clocks. This past summer I lived with a few other people and they would come into my room in the morning and yell at me, because my old alarm would wake them up but I would sleep through it, despite the fact that it was positioned right next to my head.
While I do not believe this alarm reaches 113 decibels or that it is louder than a jackhammer, I will say that it is much louder than your standard alarm clock. The vibrator works very well and is guaranteed to wake up even the deepest of sleepers. You can put it under your mattress, which will cause the majority of it to vibrate, or you can place it against a solid object which will cause a loud vibrating noise. I opted to keep mine under my mattress.
Many people have posted that their units burned out or that it kept time incorrectly. This is because they failed to look at the directions. In the directions that come with the alarm clock there is information detailing a switch on the backside of the unit. It is labeled 24hrs 50hz, 12hrs 50hz, and 12hrs 60hz. This switch not only controls the time format(12 hour vs. 24 hour), but also controls the tuning of the internal electronics. In European countries, 24 hour time format is standard, and wall outlets alternating current runs at a frequency of 50hz. In America, most people use the 12 hour time format, and our electrical outlets operate at a frequency of 60hz. What this means is that if you have this switch in the wrong position, you run the chance of damaging your unit, and you will notice that the time will not be accurate(it says this in the manual).
The only thing that keeps this alarm from getting five stars is the face that I can't use the 24 hour time format. I live in the US but work on a military base and have become accustomed to the 24 hour time format.
tldr; This alarm will wake you up, just make sure to read the manual or you run the risk of incorrect time and a fried alarm clock.