Gabriel Bestard-Ribas got tired of his house keys scratching the smartphone in his pocket, so he combined them.
The result was a Goji lock, which senses when your smartphone is near and not only unlocks a door but greets you by name.
It's just one of the "smart locks" on display in Las Vegas.
"My keys were always scratching my phone, so I thought why not build them in," said Bestard-Ribas, founder and chief executive of San Francisco start-up Goji.
His creation fuses mobile internet technology with centuries-old lock mechanics. A free Goji application installed in smartphones uses Bluetooth connectivity to let the lock know a person is near and, if it is a resident or someone given a "digital key", a personalised welcome message is displayed and the path is opened.
A camera built into the lock takes a picture of whoever is arriving. Images of visitors as well as alerts regarding entry are relayed to residents' smartphones through home wireless internet connections.