I had this problem when I first got my 08 535i. I went to the car in the morning and all 4 windows and sunroof were open. Another time my trunk was open. In both cases it was my fault when I sat down with the key in my pocket. I now put the key in a bowl and it hasn't happened since. But don't leave the fob near the front door since thiefs break into homes just to get the keys to your ride.
The fob pouch may work but I find it is very bulky so didn't buy one.
2012 BMW 535i X-drive; Space Grey/Black Dakota, Fineline; Executive (Auto trunk, NAV, HiFi Prof, Lumbar, Rear Cam, SIRIUS, Voice), Technology (Blind Spot, Hi-Beam Assist, Lane Departure, Surround View), APPS, Rear heated seats, Tint.
Retired: 78 300D, 81 300SD, 87 190E, 88 Porsche 924, 89 260E, 93 300E, 97 Volvo 850, 98 E320, 03 BMW 325iT, 02 C230 Sport Coupe, 08 BMW 535i