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Apologies if this isn't on topic; let me know and I'll remove it.

Having keyless fobs is quite wonderful, but it does seem easier to accidentally put the key through the laundry cycle because it never comes out of my pocket and I thus forget it's there

Having fully washed and dried the current car's fob for this, third, time (the previous two times I've had a moment's realization and stopped the cycle before too much water got into the fob) I cracked it open to find a few of the solder joints looking a bit furry and corroded, battery was ruined (never seen rust around the edge of the -ve of a CR2032 before), but scrubbing with distilled water, rinsing and blowing off with the air compressor and replacing the battery seems to have produced a working fob.

I'm not sure how many time I'm likely to be able to repeat the stunt so I'm looking for a way to protect the board from the laundry. The rubber seal on the housing itself is intact, but seems poorly designed (ford fob) compared to my previous (volvo) fob that went through the wash many times and was always bone dry inside

I'm hence looking to find out of the board itself can be coated with something protective. I'm not too bothered if this coating cannot protect the mechanical switches as they can be replaced if they get ruined - I'm more thinking the antenna coil, ICs etc. I'd also have to scratch it off for the battery terminals, so i guess I'm looking for something that adheres to the board, and cannot be cleaned off by up to 60 degree water but I also need the coating to be thin because there isn't a lot of space inside the fob. I read some sugggestions here but epoxy/urethane don't seem thin enough, "acrylic conformal coating" is a bit vague and I've a doubt marine grease would survive the wash temperatures without causing issues for clothing

I'm not averse to dipping the entire fob external housing in plastidip, but the result would be a bit ugly; I'm keen to know if a PCB based solve would be more workable

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    \$\begingroup\$ Put the fob in a small ziploc bag. Or attach the key fob to a larger fob made of, for instance, sodium, or perhaps aluminium with a 'DANGER, SODIUM' label on it, which might get your attention before the wash. \$\endgroup\$
    – Neil_UK
    Apr 24, 2020 at 10:53
  • \$\begingroup\$ Just get in the habit of emptying your pockets before you wash anything (surely). \$\endgroup\$
    – Andy aka
    Apr 24, 2020 at 10:55
  • \$\begingroup\$ Hah, love it. Since asking, I've found another couple of questions along similar lines that suggest looking into conformal coatings (who knew there were so many), and also mentioned clear gel nail polish.. (Mmm solvents!) so this question might reasonably be a duplicate, but for the temperature aspect \$\endgroup\$
    – Caius Jard
    Apr 24, 2020 at 10:56
  • \$\begingroup\$ @Andyaka I blame the corona - some of the people I live with are a bit more panicked about it than I think a human being should be, and "get back in from the doc's (a non viral related routine appointment), take clothes off and put straight into the washer" was what happened in this case :) - but all in, I'd rather spend $10 on a can of something to coat the fob with than whatever $00 the dealer wants to charge for coding up a new fob.. \$\endgroup\$
    – Caius Jard
    Apr 24, 2020 at 10:57

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Usual way we make sure designs are sealed even if they have gaskets is to run a bead of normal gutter silicone along the seam on the edge, however in your case you would also want to cover the led light duct and the rim of the buttons,

This way its not too difficult to reopen, but if you clean it back to be smooth to the surface will stay put,

Have mainly only done this on outdoor monitoring systems, so not too sure how much other things in your pocket might hurt this,

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    \$\begingroup\$ Common silicone sealants release acetic acid as they cure. This is a very bad idea if it is in contact with electronics. \$\endgroup\$
    – Elliot Alderson
    Apr 24, 2020 at 11:56
  • \$\begingroup\$ On the outside plastic housing, "The seam on the edge", the light duct and button are also going to be plastic or rubber, \$\endgroup\$
    – Reroute
    Apr 24, 2020 at 11:57

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