The iPhone 6s and iPhone 6s Plus were unveiled on September 9, 2015 during a press event named "Hey Siri, give us a hint." at the 7,000-seat Bill Graham Civic Auditorium in San Francisco. The hardware design of iPhone 6s is nearly identical to that of iPhone 6, although the chassis is now made of a stronger aluminum first used by the Apple Watch Sport to improve its rigidity. It is available in gold, silver, space gray, and new for the 6s, rose gold-color finishes. iPhone 6s is powered by the Apple A9 system on a chip, which the company stated is up to 70% faster than Apple A8, and has up to 90% better graphics performance. iPhone 6s has 2 GB of RAM, more than any previous iPhone, and also supports LTE Advanced. While the capacities of their batteries are slightly lower, Apple rates iPhone 6s and 6s Plus as having the same average battery life as their respective predecessors. The iPhone 6s features technology known as 3D Touch; sensors are embedded on the screen's backlight layer that measure the firmness of the user's touch input by the distance between it and the glass, allowing the device to distinguish between normal and more forceful touches. 3D Touch is combined with the Taptic Engine vibrator to provide associated haptic feedback. iPhone 6s features a 12-megapixel rear-facing camera, upgraded from the 8-megapixel unit on previous models, as well as a 5-megapixel front-facing camera. It can also record 4K video, as well as 1080p video at 60 frames per second. The camera app's "Retina Flash" feature allows the display's brightness to be used as an impromptu flash on images taken with the front camera, while "Live Photos" captures a short video alongside each photo taken.