Eventually, Rahman hopes, several “Internet of things” devices could respond to your needs by taking data from activity-tracking bands. Right now, he says, your thermostat has no idea if you’re feeling hot or cold, let alone whether you’re hot because you went for a run and will soon cool off or because it’s the middle of a long heat wave that calls for the air-conditioning to stay on. Rahman’s vision, he says, is for the gadget on your body to lend such context to the devices around you—giving you yet another reason to never take it off.