I think this situation has a 2-part answer
@ejeter45.
Let's tackle the first one:
today I got in my car and left the house without my key fob
In order for this to happen, your key fob had to be in close proximity to your Model S.
My wife and I used to live in a house without a garage so we had to park our cars on the street in front of our house. We always placed the keys on a key bowl right at the door and never had any issues, but the first day we brought our brand new Model S home, we realized that it didn't auto lock itself due to the close proximity to the bowl where we placed its key fob. I was able to go out, press the door handle, -they extended-, got in the car, pressed the brake pedal and drive off with the key fob still in the bowl inside our house with all the other keys.
Safe to say we moved the keys to another part of the house. Fortunately we realized this on the first day of ownership and we lived in a gated community, so no harm done.
My recommendation here would be to keep your key fob further away from your Model S so the next time you don´t have it with you, your car will display the "no key fob" message you saw when you came out of the store.
Now the second part:
I don't understand ....I thought you had to have keyfob to drive.
The "Remote Start" feature on the Tesla app was first introduced in September of 2014 with app version 2.0.1 for Android and iOS, and required Model S' to be in firmware version 6 (we are currently in firmware version 11).
As
@pilotSteve mentioned, it's a great feature if you are on vacations and you need someone to move your car, or if your key fob got lost or stolen so you don't get stranded. (If your key fob runs out of battery, you can still use it dead by placing it near the passenger windshield wiper to unlock the car, and near the 12v outlet in the center console in order to start the vehicle):
But anyway, the most important thing to consider about the Remote Start feature of the Tesla app is that
BOTH your Model S and your phone need to have an active cell data connection.
The way this feature works is that when you open the Tesla app on your phone, your app pings the Tesla servers in the mothership, which in turn they ping your car via its cellular connection (AT&T network in NA) in order to wake the car up. That's the "click-click" sound you hear when the HV contactors close.
Now that the car is awake, it has an active connection to the mothership and is now able to receive API commands from your phone app.
The "last seen" message you see in your Tesla app tells you the last time your car contacted the mothership. This was just recently changed this way with version 4.12 of the Tesla app, as it previously used to tell you the last time YOU contacted your vehicle (opened the app).
It's important to highlight the need for cellular connection because people often leave their house using the Remote Start feature and park their Teslas underground, where the car sometimes looses cell connection. This sometimes also happens when you park near a source of high frequency interference such as a radio station antenna, high voltage power lines or near an airport control tower.
the app on our phone could communicate via wifi and/or bluetooth.
Unfortunately on Legacy Model S/X (the ones with the vertical screen) the app only communicates with the car via a cell phone data connection.
On Palladium S/X (the ones with the horizontal screen) as well as 3/Y, the Tesla app is able to communicate with the car using Bluetooth and cell connection. No WiFi interaction between the car and the app on any Model.
