Garmin 305 heart rate strap waterproof?

I don't know that garmin advertises it as waterproof but I've worn mine under tri top, under a wetsuit in the water with no ill effects.

Strap will be fine in the water.  

As for the 310 working in water, it will record times well, but GPS and HR not so much.   If you want GPS out of the 305 or 310 I would suggest using the trick to put it in your swim cap in a baggie to keep it protected.  

Leaving it on the bike and swimming with the strap is a good solution if you dont care about your swim time or having it on a different device. 

have worn during races in the water with no issue but did not wear the 305 in the water

I posted this a few days ago as well and I also called Garmin...

I just called Garmin and they told me the one I have with the plastic center and rubber back that came with the 305 is NOT water proof. They do sell one that is an "upgrade" I guess and is in fact water proof

Part # is 010-10997-02...$69.95 direct from Garmin. He suggested searching the part # on the internet and buying it that way.

Just FYI

So if you dont wear the watch in the water you put it on in T1 I assume? Do you ever run into problems with one more thing to do in transition? Or could you leave it in your bento box for the ride and then strap it on when starting the run?

Want the truth?

Skip it entirely...  I used my Garmin for maybe 2-3 races and something always went wrong.  Battery was dying during my HIM, I messed up the "multisport" function.  It doesn't include your swim time...  It really never gave me much more than what my bike computer and my watch could.

I use my Timex watch/HRM.  Start it at the gun, hit lap ever time I cross a timing mat, keep tabs on my HR...  Bike computer to keep track of speed and distance and the mile markers during the run to do the same for that.

I agree, having the Garmin data is nice, but not worth the hastle in the long run during a race.

Like others, I just:

1) Swim: Have the HR strap under my tri suit/top.  Despite what someone received from Garmin support above - both the classic and premium HR straps are indeed waterproof.  It's just that neither will successfully transmit HR while underwater (it goes about 2-3).

2) Bike: Once I get on the bike, the HR strap is instantly picked up (it's pre-paired of course) and then the Garmin is ready to go.  I leave the Garmin on my bike.  If you're afraid of someone nabbing it - just toss it in your bike shoes with your bib over it - problem solved.

3) Run: Once transition to run is complete, it's still on me with my HR monitor still ticking away.

Super simple.  I did write up a post last year for how to race with your Garmin - may be of interest.  In some ways I wrote way more in depth than just above, but if you boil down all my rambling, it's essentially just the three steps above.