The best replacement for headphone is earphone.

The best alternatives to headphone are rated as following:
★★★★★  earphone
★★★★★  headset
★★★★  speaker
★★★  line out
★★  earbud
★★  iem
★★  earbuds
★  headphones
★  in ear
★  fp headphone
★  line level
★  line out voltage
  wired headphone
  audio out
  silent cinema
  beats by dr dre
  cmss-3d
  line output
  insert earphone
  microphone

Your alternative for headphone is not listed? Suggest!
Speaking about headphone, one probably shouldn't forget about mic.

Other search terms related to headphone and their ratings are:
★★★★★ mic
★★ wire
★ mike
You have in mind a companion for headphone and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of headphone in all years. Click on graph for more.
headphone
earphone
headset