Has anyone built any kind of sensor that you can place below your car that, when the car is over the sensor, would indicate that the car is parked and show a light? Kind of like what you see at large shopping centers except no where near as elaborate? I think this would be a great system for Home Assistant, but not sure if the actual tools (magnent? Lux? sensors) exist to indicate when a car is parked over the top of it and then have it transmit to HA that the space is taken…
Is it really that you want to know if a parking space is taken, or do you want to know if a certain car is there? The latter can be done with a tile or other BLE tracker.
I just want to know if a car is there, not a specific car, just if the spot is taken
Magnetometer.
That’s the kind buried in the pavement. It detects the presence of a large (ferrous) metal object like a car because the car alters the sensor’s magnetic field.
Unless you’re able to easily bury it in your driveway (re-paving it soon?) it’s not the most convenient method (albeit quite durable and foolproof).
Ya, I know that is what I need but not sure if anyone has made it integrate into HA.
Not planning to redo my garage any time soon, just looking at feasability. I’m pretty sure that I could back up well enough not to run over it 
if I do put it down just on the ground under my car…
As mentioned, they’re meant to be buried (out of sight and out of harm’s way).
My guess is the device, at a bare minimum, acts like a binary sensor but I imagine it can be more sophisticated than that. Ideally it would support MQTT over Wi-Fi and then it would be trivial to integrate it with Home Assistant. However, I suspect it’s not that simple and integration would require additional hardware (like ESP8266).
If you simply want to detect the presence of a vehicle in your garage, their are ultrasonic sensors designed for this purpose (search for ‘garage parking sensor’).
Ya I figured that it wouldn’t be an easy solution nor would one be available to use out of the box
Each esp32 has hall sensor. I am not sure if this could be leveraged. ESP32 Hall Sensor — ESPHome
You could 3d print a thin case to hold an esp32 and stick it to the garage floor. Maybe.
This uses a nodeMCU with ESPHOME and some ultrasonic sensors to do this, go to 5:35
We have the parking sensor in our garage. The sensor is an ultrasonic distance sensor mounted on the ceiling. The ceiling mounting position is better than something on the ground since it’s not subject to the physical damage and wiring is more straightforward.
You can implement one easily with ESP8266/ESP32 and ESPHome firmware.
I use Sharp IR distance sensor hanging over the parking spot to detect car presence in garage. As output it provides voltage changing depending on distance to obstacle, so it changing if car is out (distance to floor) or in (distance to car roof). It is connected to Fibaro Smart Implant (Zwave) analog input. Works perfectly fine for ~3 years already.
Thanks Everyone, I was hoping more for the magnometer idea that could be used for multiple parking spots in an open parking lot…