power down system

Hi there,

I'm working on a project for which I'm using servo motors, temperature, pressure sensors and an accelerometer. One of the requirement is to have an automatic shutoff function where I need to power down the systems and illuminate an LED (without disconnecting anything physically) whenever a sensor value reaches threshold etc. I would appreciate if anyone could guide me on how to go about this in most simplest way.

Thank you

Not without any details of your systems and how they are powered!