Home Alone

Alright, so I'm sitting home alone upstairs (My garage) playing runescape in a nice warm comfy environment when i appear to hear "The lights are on but nobody is home". It scared the hell outta me and a walked across (making heaps of creeking noises) had a look out the window, but couldn't see anything. It just happened again, except i thought I heard knocking. For once in my life, I hope i'm going mentally nuts. My parents will be home soonish and I'm quite literally freaking out. It's even worse that on monday we had "shady people" pissing on our hedge and on wednesday, someones house got broken into. I'm lucky that if something does happen, my hand is about 50 cm away from a phone, so I can take actions. Time is tcking and nothing has happened for 5 mins now...