I'd love to know the answer because it's one of my favourite nightmare scenarios. Many modern elevators are designed to keep you inside the box, on the grounds that if you get out of it you might fall down the shaft. The elevators in the World Trade Centre were like that. On 9/11 they malfunctioned and trapped many people inside. Some estimates blame 10% of the WTC death toll on the elevators. If the building is on fire, take the stairs.

I believe a whistle would help people find you better than shouting. A mobile phone is worth a try - I presume Chen didn't have one.

Some tools could help you escape despite the security. I EDC a Serbertool M4 which is puny but maybe better than nothing. When in town I usually carry a Leatherman Juice CS4. I also EDC a piece of hacksaw blade which serves partly as a striker, but which I carry mainly to have some hope of cutting metal in a situation like that.