Once a thing of the future, identification systems based on biometrics are now pretty common. Things like fingerprints, voice recognition and retinal scans can be used to positively ID you and provide entry to a given device or function. Adding a little bit of uncommon to the biometrics equation, Apple recently applied for a patent for a heart-rate monitor system.
The cardiac monitor would be included in Apple devices such as the iPhone and would automatically recognize the user based upon his heart beat. It would be capable of sensing various measures of the heart (heart rate, amplitude, etc.) and using them to ID the person.
The hardware would be built into the device casing and the heart beat would be picked up as soon as the user touched the device, enabling the user to unlock the device by simply holding it. Perhaps the most interesting (and eerie) part of the technology is that it would be able to "sense" the individual's mood based on the heart rate and respond with content directed at said mood. As long as it doesn't offer links for weapons or poisons when you're feeling sad or depressed, this could be an interesting little feature.
In the application, Apple indicates that the monitor could be used for a variety of products including digital media players, cell phones, laptops and fixed electronic devices (i.e. desktop computer).
Apple explains it much better than I ever could: "“The electronic device can include a heart sensor having several leads
for detecting a user’s cardiac signals. The leads can be coupled to
interior surfaces of the electronic device housing to hide the sensor
from view, such that electrical signals generated by the user can be
transmitted from the user’s skin through the electronic device housing
to the leads. In some embodiments, the leads can be coupled to pads
placed on the exterior of the housing. The pads and housing can be
finished to ensure that the pads are not visibly or haptically
distinguishable on the device, thus improving the aesthetic qualities
of the device. Using the detected signals, the electronic device can
identify or authenticate the user and perform an operation based on the
identity of the user. In some embodiments, the electronic device can
determine the user’s mood from the cardiac signals and provide data
related to the user’s mood.”
The technology has only been seen in the form of Apple's patent application, so it may or may not find its way into production. However, it offers a glimpse into an interesting future where technology continues to make life that much more convenient.
For all the technological ins and outs, you can read the full patent application at the USPTO.