Jen, you can use a wristwatch
Jen, you can use a wristwatch without "pods" to measure cadance. You need a watch that displays speed without GPS.
Find out how to set the running stride length in your watch. With stride set at 36 inches, and the watch reading speed in miles per hour (mph), you get the following cadences at displayed speed:
{cadence,displayed speed} = {{150, 5.11}, {160, 5.45}, {170, 5.80}, {180, 6.14}, {190,
6.48}, {200, 6.82}, {210, 7.16}, {220, 7.50}, {230, 7.84}, {240,
8.18}, {250, 8.52}}
These watches estimate speed from your arm swing to get the number of strides per minute (cadence). It works as long as your arms swing at the same rate as your legs. You must enter your stride length as input data so the watch can figure out speed. Its not so good at getting speed right because stride changes, but its very good at getting cadence right.
I try to keep the speed between 6.10 and 6.30 mph (179 - 185 strides per minute), but within that range its whatever I feel like running. Its surprising how just running, checking the watch only occasionally, I find the speed rock-solid at 6.14 mph = 180 steps per minute. 180 is a natural cadance, at least for me.