Project Ara was announced last year, it is a modular smartphone system that allows you to swap out components such as processor, camera, battery and much more by upgrading instead of purchasing a new phone.

Google engineer Rafa Camargo demo-ed a functioning Project Ara smartphone by sliding modules into a frame, turned it on, then added a camera module and took a picture of the audience during the ATAP keynote at Google I/O 2015.

Project Ara demo-ed

From the video we can tell some of the module components are hot-swap, meaning it does not required power off to change/add the module.

Source: TheVerge