Fit bit

Fit Bits use an accelerometer to measure those steps. This accelerometer uses the changes in your arm swing to determine your "steps". The count you have at the end of the day is literally how many arms swings you had, rather than actual steps. To be fair, most normal humans have one arm swing per step, so the number is generally accurate.

However, you won't get an accurate measurement if you wear the Fit Bit on your left wrist and that arm is holding on to a med cart all day. I've seen two co-workers mount their Fit Bit onto a stretchy hair tie, and put it on their ankle. It seems odd at first, but they're likely getting a more accurate step count that way than the rest of us.

A shift manager I work with uses a Map My Walk type app on her phone, so she has a mile number at the end of the day rather than a step count.