Does anyone knows how long the transmitter will go on?
I have him now for one year.

I used one for about 14 months before the signal started having continual issues. Reports online indicate ~12 months is a typical life expectancy for these, which works nicely with the warranty expiration.

I’ve had mine for almost two years, and it still seems to work fine. However I am noticing a few more out of whack numbers lately.

I replaced my entire Dexcom unit in late February 2011. That's a little over 18 months ago and my transmitter still works fine.

I have had mine for 14 months now and it just had a complete system failure. Had to buy a whole new kit. They said it depends on how well you take care of it but I know I baby mine. I have also heard some peoples lasting 3+ years. So it just might be luck of the draw.