Wearing a step tracker on ankle for more accurate activity tracking

My only outdoor activity, and the majority of my daily exercise is biking to and from work.  I used to wear an ANT+ Garmin chest strap paired with the ANT+ iPhone 4 adapter to measure my heart rate and estimate my caloric expenditure.  The readings I got in the Digifit report was accurate when it worked, but had a few problems:

• Initial sync with the my iPhone took up to a minute.
• Unless I wore my iPhone on my arm to keep it close to the sensor, it was prone to losing connection.  The monitoring application I used--digifit--was not smart enough to recover from intermittent connection drop, so I would sometimes lose more than an hour of riding record.

I got fed up, and stopped using it.

Recently, I started working at Jawbone--specifically on the wearable band firmware.  One of the perks is a free UP3 band, which monitors sleep, estimates steps, calory, and resting heart rate.

Because it is always running, I don't have the hassle of maintaining connection with my cell phone (except for a daily sync with the cell phone).  I think it is a wonderful hardware, but it is not sensitive enough to accurately monitor my biking activities, because my hands are moving very little when I am on my bike.

One workaround suggested to me is to put it in my pocket.  Since my thigh is moving up and down when I pedal, it can count steps while in my pocket.  Another workaround was to get an UP MOVE, and clip it to my bike shoes.

But in truth, I don't like wearing anything on my wrist, so I thought: why not just wear the band on my ankle?  Then it can detect my heart rate just like when it is on my wrist!  The problem is that the band is too short to wrap around my ankle, which is 8 3/4 inch, as measured with a string around my ankle.  If my ankle circumference had been half inch shorter, a fully extended UP3 (see the picture below) would probably wrap comfortably around my ankle.  I tried it, and found it too tight.  When the clasp is at the longest position, there is actually more than a half inch left from the end of the rubber band--I just could not get there because of the bio-impedance sensors in the way, as shown below:

WARNING: I do NOT speak for Jawbone in describing my hacking below.  Doing what I did will probably void your warranty, so please don't blame me or Jawbone if you break your UP3 following my example.  That said, UP2 doesn't have a bio-impedance circuit in the rubbery band, so you probably will not damage it.

So I took off the adjustment clasp with a pair of pliers, and flipped it around 180 degrees to have it FACING the other end of the clasp pair, as shown below:

Further bending of the metal made it feel comfortable around my ankle, as you can see below:

I am happy with the result: the UP3 band is working as well as it did when it was on my wrist, and of course now accurately counts my pedaling.  I was lucky: if my ankle circumference had been even half inch longer, the band would have felt too tight.

3 month update

The clasp is looser than before, and regularly comes off during sleep.  I don't recommend this hack for others.  I took a plier and tightened up the clasp a little, and now it's very secure.