During my travels to Hong Kong, we got a Octopus card. You load them up at a local MTR station, and off you go. They're usually popular with public transport there (MTR, buses and even trams!), butsome retail chains also allow you to use Octopus cards too. Basically when I had to go through the MTR, I would take out my wallet and place it over the yellow scanner, and place it back. Quick, short, simple and fast. It's pretty secure, unless you lost your grip on your wallet.
If you got, say a purse or maybe a bag, it was strong enough to pick it up (if the card was near the bottom of it of course), and it was instantaneous.
The Snapper implementation on the bus looks good (though it's vertical... I would have preferred a 45 degree angle - it's easier to hold it down than upright)