Anyone tried this?

Well, I inadvertently left my RRS key in my jeans and my partner machine washed them without checking. Mad panic when I worked out where the key now was - hanging up drying - and a rush outside to check.

Fortunately car unlocked and started up just fine

One relieved owner...

I would recommend you hang the key up by the ring, overnight to allow any water the chance to drain out.

Put it in a tub of dry uncooked rice! Will take any moisture out  2003 BMW M5 - 5 Litres of V8 Optimax Slurping Goodness in Carbon Black

2013 SDV6 HSE Black Edition- Orkney Grey with Ebony & Ivory. LR Facelift RAI, Genuine G4 Expedition Rack, 4x Warn SBD-160 Spotlights, Warn 9.5XPS Winch, Mantec Underbody Protection and Sump Guard, Full Easy Lift Suspension Module, LR Light Guards, Light Force HTX230 Hybrid spotlights, 18” Compomotive PD1881 on 265/65/18 BF Goodrich KO2, ARB fridge, TuffTrek awning 😎

The non keyless entry keys are waterproof.

If there's any risk water might have got in, I'd be opening and giving it a flush with electrical contact/cleaner spray. Water itself doesn't pose too much of a problem (provided you don't try to use it when wet - the dry rice works well) but I'm not sure what effect any soap residue would have for the future, it might speed corrosion which then is your concern. Remove the battery when flushing as those contacts are sure to corrode in future.

But as posted above, hopefully it is waterproof (resistant) so is all dry inside

Dennis 13MY Range Rover Sport Autobiography SDV6 - mine
14MY Range Rover Evoque Dynamic SD4 Black Pack - wife's
99MY Defender 90 TD5, Soft Top Conversion - my toy, and bairns favourite