Heart Rate Measured but no chest monitor and fenix 5 on handlebars

Thanks Ronand...was able to look up the sensors per your recommendation....took a long time to decipher all sensors I used but good learning experience...data shows the HRM data being recorded for 20 mile activity yesterday did not include the HRM Run Chest Strap; HR data derived from Fenix 5X wrist monitor strapped to a plastic support on the handlebars.  Considering bicycle doesn't share my pulse, most concerning find is plausible data (a.k.a. HR increases/decreases with climbs/cadence) and within a reasonable range based on effort....making me wonder how much plausible data vs accurate HR data I've been collecting and targeting over the last several years. Appreciate the great guidance!

Optical HRM accuracy is pretty dismal on any device once the heart rate is elevated to any degree. Its reasonably ok for walking but nothing any more strenuous than that.   If you want accuracy just use the chest strap.

This has been reported several times on other watches and the results can look quite realistic too. I’ve seen it from a 945 and Fenix 6. Easy to speculate what might cause this to happen but hard to prove. Vibrations perhaps? Similar has been seen when watch is placed back facing down on some surfaces.  

if you wear a strap most of the time then most of the data will be good data. Of course best way to avoid this phantom data is to connect a chest strap when the watch is on the handlebars.