Can you activate Siri over a bluetooth microphone without pressing a button? I ride a motorcycle with a full face helmet and gloves.  The gloves do not allow you to press the home button on the iphone despite it being mounted right in front of you on the handlebar.  The bluetooth mic at my chin is impossible to reach with the gloves on and even if you cram your hand under the chin guard you would be guessing and fumbling around trying to press the tiny mic (activate Siri) button).

From a safety perspective, the rider should be able to keep both hands on the controls and simply say "Hey Siri" into the bluetooth mic inside the helmet and have Siri activate.  I have been searching the internet looking for this capability and this forum is all I have so far found.  Sadly, no answer appears to be available to activate an "always listening" bluetooth mic.  

Google assistant apparently can do this from what I have read, but users complain that the headset/mic battery is dead in less than 2 hours.  I would prefer the longer life of AirPods without th battery drain. 

Is anything possible to keep my hands on the handlebar and use and iPhone with any headphones, Apple or third party?
Did you ever try the Senna 30K? Here you can see it in action: https://www.youtube.com/watch?v=qrEVgfatyjM This is pretty much what you are looking for. A Bluetooth headset activated by voice and make Siri do what you desire.