“I wonder how well an iWatch will do starting my 57 Chevy Bel Air?”
You don’t need a key (or iWatch - semiconductor was invented in 1958) to start your 57 Chevy :)
“Aftermarket”! ... think aftermarket! ... :-) ...
Brings back memories of the Chevy cars I owned back in the 1960s, like my '57 coupe. A key for your Chevy would often work on several of your friend's cars. If you weren't carrying the key, cross a couple wires under the dash and start by briefly tapping a third wire. Or under the hood via the starter solenoid. Once when I was 17 parked at a drive-in restaurant, a pretty gal came up to me and asked if I could hot-wire her car. Her date had argued and taken her car keys. So I lay on the floor under the dash while she and three other pretty gals in the car watched me. Hard to concentrate with a gal in a mini-dress sitting in front! Got a safety pin from her, pierced two wires, tapped the third (perhaps purple), and she was happy as can be. So happy she thanked me later (another story).
Side note: you can rig an electronic gadget to start your '57 Chevy that operates via an Apple watch. Or other remote, been done for years with a few bucks in parts.