Phone holder that reminds people to limit smartphone usage

Use Scenario

When I'm working, sometimes I would start checking my phone mindlessly before realizing a long time has passed. Therefore, I hope to design a phone holder that gives out warnings when I pick up the phone.

Input: 

- Force Sensitive Resistor (FSR): sense the weight of a smartphone

- Switch: turn the light system on/off

Output:

- (when a phone is sensed on the holder): blue LED on / red LED off

- (when a phone is NOT sensed on the holder): red LED on / blue LED off