Well I can't open the car with my keys in the house approximately 15 feet away so to relay the signal they'd have to be in my house and if they are in the house they can just take the keys.
Misconception proven.
The thieves use two parts in relay theft. 1. A scanner/booster 2. A receiver.
The distance from the physical key to your car is totally irrelevant, and the distance from the scanner/booster to your key is only marginally relevant. The only constant that matters is the the distance from the scanner/booster to the receiver.
The receiver is always by the car (waiting for the signal so it can pretend to be the key), it's the scanner/booster that throws a signal to the receiver. The scanner/booster has two range elements, it can throw a captured signal to a receiver that is up to to 100m away, but more importantly it can grab signals from a key that is up to 25m away (depending on what is in between the key and the scanner/booster.
So a thief will normally scan the front of the house for ease (and because most people keep their keys by the front door), but if it's a big house, or it has particularly thick/dense walls, they might go round the back/side as shown in other youtube videos.
This works in car-parks, where you may get followed across a car park and the signal thrown to the receiver, or it might happen at home.
Relay theft is must-function, and multi-scenario.