A lot of information about this device online is misleading. When I first heard about this, the site I was reading claimed the transmitter didn't have a battery, and used the energy from the foot impact to power the burst transmission of the device's ID. This is what got me excited about the device in the first place: that it was so simple.
Other places I've read say there is an accelerometer inside. While not entirely inaccurate, it is again slightly misleading. It does not have an accelerometer the same way a Wii controller does. It has a piezoelectric sensor. (See SparkFun's Nike+iPod Dissection page)
I am not entirely confident that I know the capabilities of piezoelectric sensors, but if I am understanding correctly, they are primarily used to detect impact, and not smaller accelerations like the Wii controller does. What I am saying is that the sensor doesn't know it is being dropped, it just knows that it hits the table.
Here is another data dump from the sensor. I tapped the sensor on the table two times every second. It's two short taps followed by me waiting for the receiver to show it received a packet.
This dump is from tapping it once per second on the table:
Something really interesting happens if you group all of the lines together that begin with AA, AB, etc. A lot of them match up! This is a re-arrangement of both dumps of data. Blue is from the "1 tap" set, red is from the "2 taps" set.
What's really strange to me is that I got a lot of the same lines, even just from tapping it not terribly accurately by hand. With that many bits, it is no coincidence that so many of them match up. This suggests to me that the resolution of data transmitted is not as great as I originally thought.