I do watersports and have a need to lock my car while I'm in the wet stuff - what's the best option with the keyless entry system? Should I put the fob in a metallic bag and leave it in the car while I take the physical key with me? (advantage: the physical key should be waterproof) Or should I get a small waterproof bag for the fob? (disadvantage: yet another dangly bit to keep track of) Open to suggestions - I used to have a spot on my gear where I attached a spare key, but that's no longer an option.
Take a look through the following thread - there was lots of discussion about this very thing. http://priuschat.com/forums/gen-iii-2010-prius-main-forum/64699-what-do-key-while-surfing.html
I inadvertantly took my key swimming once. Much to my suprise, it worked just fine afterwords. (I don't recommend testing this on purpose though!)
A couple of weeks ago, my Prius fob went soaking with me for about 20 minutes in hot springs on the Rio Grande river, before I remembered it was in my pocket and took it out of the water. About an hour later, when we got back to the car, it worked and continues to work. But I don't plan to do it again, unless I'm stupid again (always a good chance).
I think you could leave the remote in the boot and take only the original key. The only problem can be that the car detects the remote even if it is in the boot. I know that if key is detected in the car you cannot lock the doors. PS. I once washed a key with built in remote to my old car (Golf TDI 2005) in a washing machine. It worked immediately after it and continues to work.