Parking in a snug garage - is it in yet?

The old classic is a tennis ball on a string hanging from the roof. Set it up so it touches the windscreen/rear window when you get to just the right position.

Sandbag or such like on the floor so the wheels hit it before the car hits the shelves

I had a 2 pieces of 2x4, one along the wall so I could park the car wheels tight to the side wall without scraping the car, and a smaller piece, about 300mm bolted to the floors the wheel wold hit it when the car would clear the door and allow it to shut.

I’ve got a piece of two by four screwed down but used to just line my door mirror with a mark on the wall.

When I was a kid the old boy I worked for asked us to clear his garage out for him and he had a tennis ball on a string. We kept walking into it and it was getting right on our tits so the bloke I was with threw it over the next rafter. Monday morning and Mr G pulls up with the front of his BMW stoved in. We’re all looking out wondering what had happened until he walked in and said a bit sheepishly “Erm did any of you move a tennis ball in my garage...?”

I used to have a champagne cork hanging from the roof, but then the garage got full of junk and the cars got too big (well not teh MX5) so the cars live outside.

Stick a squeaky toy chicken at bumper height

This is all wrong.

Tennis ball on a string
Lump of dead tree bolted to the floor
Alignment mark on the wall.

Where's your imagination? No style points for pointless complexity in any of those answers.

Where's the CCTV Bluetooth linked to your phone that's mirrored to the screen in the dash?
An Arduino or Raspberry Pi running pattern recognition software to send messages to your phone providing the distance to the critical static element accurate to the nearest micron?

I'm disappointed today's youth. These are all Grandad's solutions. PAH!

Plank of wood on the floor for the rear-most wheels helps. I like the suggestion above about carpeting the walls! Says me without a garage though.

My grandad had the tennis ball from the roof and carpeted walls too (leftovers from the living room - nice!)

Later on he bought some kind of electric traffic light style sensor from lidl which I thought was disappointing because the old trick worked perfectly.

When they bought the house they had an isetta and his last car was a Peugeot 307 so it was getting a bit tight.