Power down feature is very handy on battery operated devices. For instance most of multimeters already have this feature allowing them to self turn off when there is no activity for some time. Check out this simple solution which uses pair of FETs and resistor.
It was originally made for Atmega328 project because author didn’t want to bother with AVR power down modes. Instead he used this simple circuit. It can be used to turn device on with switch this is where P-FET part plays role and turn off with N-FET. Turn Off signal wire comes from AVR pin market as 5. While device is powered N-FET has to be on with high gate signal. When N-FET gate signal goes low device turns itself off. This can be used on any device where possible to get such signal conditions. Or simply use in microcontroller circuit by adding some delay count after inactivity.