No key detected in ford focus 2013

Did you lose the key it came with? There is a chip inside the black part covering the handle of you car key. If the chip is not detected then the car will only let you use the spare key to get inside.

We found it was our cell phone too close to the key - move the phone away and then try it - worked for us every time

In the spot where a normal key would be inserted to start the car (should see a large black circle) you should hold the key fob on the circle and then push the button to start with your other hand.