Sorry guys but I need to ask the ladies a question. I use the X2 which has the Dexcom integration. I wear my Dexcom transmitter on my abdomen. When I put my pump in my bra, which I do when I wear a dress or a skirt, the pump no longer reads the Dexcom. I get the red symbol that it is not receiving a Bluetooth signal. It’s really not very far away from the transmitter. I called Tandem and they are sending me a new transmitter. My transmitter is only a month old, but I’ll try a new one. Has anyone else had this problem? Or does it work for anyone else when you wear your pump in your bra?
Not a lady, and I’ve only had the X2 for a few days now, but thought I’d share my experience anyway 
… I typically wear Dexcom transmitter on the back of my arm. I’ve been wearing the X2 on my belt (with clip) and I’ve noticed that when the X2 is on the opposite side of my body from the Dexcom the signal is spotty for some reason (same red symbol you mention). I thought it was odd because I have my Android phone hooked up to the transmitter too and my phone could be across the room and still get readings from the Dexcom. So I’ve been making sure I keep the X2 on the same side as the Dexcom and it’s been no issues since. Good luck!
Yes, I’m very disappointed with how close the X2 needs to be to the Dexcom transmitter. It’s not a transmitter limitation, because as you say, ones phone can be across the room.