There are five sensors, including a compass, accelerometer, gyroscope, GPS, and ambient light sensor. All five of the sensors are required for a convertible tablet to be branded as an Ultrabook, and three of the five are recommended for a regular laptop branded as an Ultrabook.

Here are the five sensors:

Compass (optional for Ultrabooks): Useful for showing which direction you're facing, so you can automatically get details about landmarks in front of you, for example.

GPS (recommended for Ultrabooks): Pinpoints your location so your device can deliver mapping and other relevant information.

Accelerometer (recommended for Ultrabooks): Detects motion and gravity--often used to protect the hard drive in case a laptop is moved or dropped. Can also give users information (e.g. travel time) based on movement.