key fob          
noun [ C ] uk/ˈkiː ˌfɒb/ us/ˈkiː ˌfɑːb/
 钥匙扣
a piece of leather or other material to which a key or group of keys is fastened
  Everything from mouse pads to key fobs with his image on was on sale. 所有印有他照片的东西都在打折,从鼠标垫到钥匙扣都有。 
  遥控钥匙
an electronic device connected to a key that is used to lock and unlock a car's doors or operate a piece of equipment
  He presses a button on his key fob and electronically operated gates swing silently open. 他按下遥控钥匙上的一个按钮,电动控制的大门无声地打开了。 
 - More examples
 - Companies had set up tables strewn with free branded pens, key fobs, T-shirts and glossy brochures.
 - Contactless smart chip technology is available in a variety of forms – plastic cards, watches, key fobs, and other handheld devices.
 - I've just opened someone else's car in the car park with my key fob!
 - High-tech car thieves could use recording devices to capture your key fob's transmitter code in the parking lot.