Any device that grabs a charge from being plugged into a USB port—that includes your iPhone—can get it's juice from mostly any powered up (it has to be "on") piece of tech with a USB connection.
If the spy scenario above does ever happen to you, you won't go uncharged. But there's other ways to use this tip to your advantage.
Some people find themselves leaving their video game consoles, like the PS3, on for hours unattended while their controllers juice up. Instead, try plugging them in to the port on your TV while you watch Top Chef.