I have a Edge 305 which works perfectly for me. The strap is a bit lose for my wife, so I shorten it with a ziptie. With the ziptie it becomes really tight, but just does not detect the HR.

Have tried electrode gel, salt water etc. Sometimes it picks up after a lot of sweating but is irregular. Have tried placing the electrodes on the back but still doesn't work.

Have ordered one for her but am at my wits end as to how to get it to work. Any suggestions?