Star Trek scanner
"Detect buried powerful magnets! See the passing gravity wave from a distant collapsar on your phone screen! Be a mega-geek! Etc." †
Star Trek machinery was pretty much wonderful, so much that was almost magical - transporter technology, flip-open communicators and phasers being among them. Who among the fans didn't secretly desire a communication device that flipped open? We all learned to say "Beam me up, Scotty!" when we needed to escape a bad situation, and "Set to stun" was still in vogue at work in the '90s. I don't remember the tricorder being among the really cool stuff, though I certainly would have loved a something that would check for Bad Things and alien lifeforms.
As the series progressed, they became smaller, with better displays and doubtless, improved technology. The few close-ups show increasing complexity over time, though the meaning of all those displays is beyond us.
No-one in the real world knows exactly what tricorders did, but they were handy portable devices that scanned the environment, a part of every planetside mission. There were several varieties - the standard, used whilst scouting in unfamiliar territory; the medical tricorder (with a teeny detachable scanner); engineering and (presumably) other specialised devices. One thing they all had in common was a multipart design - the main body, a hinged upper screen and a specialised section contaning additional scanners and detectors.
My tricorder
I recently obtained the T-Mobile G1 phone, and geek that I am, one of the first "fun" applications I installed was...a tricorder. It does actually use the phone's inbuilt compass and accelerometer as well as GPS, wifi and cellphone signals to give useful information. Not that I could navigate using one, but it's handy for checking signal strength, finding open wifi networks and examining GPS co-ordinates and altitude.
Now there are, of course other and possibly better ways of getting this information, but who cares? This is fun.
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There's a picture of the application at http://tinyurl.com/cwepbu
†http://code.google.com/p/tricorder/
http://en.wikipedia.org/wiki/Tricorder
http://memory-alpha.org/en/wiki/Starfleet_tricorder