After several days of having my heart rate monitor mysteriously shut off while out riding my bike, it occurred to me when I got home yesterday that it was happening in the same general area each time - somewhere in South Park.

The monitor is narrow band I wear around my chest, with the display on my wristwatch, connected to each other wirelessly. I have the watch set to beep if I exceed a rate recommended by my doctors; it also will beep to let me know it is shutting off, which it does automatically if it's not getting a signal because I've taken off the monitor.

This lack-of-signal-thing made me think that there is some kind of interference blocking the radio signal from my monitor to the wristwatch - a cell phone suppressor, or secret military technology, probably, hidden among the cafes and taverns.

So today when I went for my ride, it was with the intent of tracking down where this is happening. The ride became a walk as I went back and forth, doing laps around blocks, hoping I'd be able to triangulate the source of the interference. I started recognizing people as I went looping around. I can't imagine what they might have been thinking as I wandered around, walking a bike while staring intently at my watch, but clearly not in a hurry.

This map shows a bit of what I found. (You can view the Heart rate monitor interference map a bit larger.)

While crossing Switzer Canyon between the northernmost marker and the middle one I had no signal, but only while on the west side of the road. When traveling on the east side, there was no problem.

The marker to the south had just a small area, maybe a few yards, where I couldn't get a readout. I'm pretty sure there's a larger patch a couple blocks south of that, but I'll figure that out later.

No mysteries solved today, but now I'm thinking about finding my way into Switzer Canyon.