If you stand on almost any mainline railway station nowadays you will be unlikely to hear the sounds of slam doors being banged shut, but rather see the almost silent sliding doors of modern coaches and multiple units. You'll hear the tones as they open and fast warning beeps as they close.
Train-Tech have managed to fit a tiny speaker onto their OO gauge cool coach light strip which simulates these sounds automatically. Not only can you light your coach but also hear these realistic sounds when the train has stopped at a station for a while.
Like all Train-Tech coach light strips there are no wires, pickups or switches, but powers the lights flicker-free from a standard coin cell battery. The lights turn on automatically as soon as the train moves and turn off after it has not moved in a while. Just remove the roof, locate the strip using Blu-tack or similar, and refit the roof - it really is that quick and easy