I never left the keys in my equipment.
I’ve never left the keys in my outdoor equipment either but sadly the master key can be purchased at the dealer.
They tried to steal my backhoe once, thankfully my battery was dead. It would be easy for them to park a flatbed down the block, steal it and away they go.
I live in the country on a coldisack street off of a road not much traveled especially after midnight. Here in Texas with the AC on and all the windows shut not one of my neighbors would here a thing, literally.
Fun fact: 1 key from each manufacturer fits most of their machines. The door keys are different, but the ignition keys are universal. Also the ignition locks are very low security, most can be easily picked with a small pen knife.