I have a 2017 Ford Mustang Ecoboost and I am aware of the hidden key inside the key fob and that it can be used to unlock the doors but can it also be used to start the engine. I know there is a slot under the cupholder to put the key fob when it dies but can you still start the engine without the key fob and just with the emergency key by putting it in the slot

 

Don't see how. The electronics are in the fob and not the actual door key. Don't think there's any way without the fob itself.

 

There should be a pocket or section that you can put your key fob. Look under your cup holder or inside the console, this will allow the NFC connect and then you should be able to start the car.