I agree with basically everyone here. When they know it is scuba gear, they relax and pass it. I've never been bothered about either weight or size. My Datamask did cause a stir once but that was from everyone wanting to try it on.
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Has anyone ever had trouble traveling with a backplate in a carry-on bag? I'm planning on putting it, and all my other important dive gear, in my backpack. The plate fits pretty well right up against the back of the pack, so there's good room for everything, and it's somewhat concealed (not to the machines, unfortunately).
I've learned to leave it on top so they don't unpack everything else to look at it.
With the plate at the bottom, they just need to take out all the lighter stuff around it swab on top of it, and swab around the plate rather than take it out.