Second, prisoners are forbidden to use any communication tools without permission, including mobile phones, telephones and the Internet. If they use these tools without permission, they are found to be serious violations, ranging from confiscation and deduction to severe confinement and strict supervision. (Of course, some places with imperfect management and facilities cannot be completely banned.)
Third, strictly speaking, any audio and video recording and playing equipment is contraband, so MP3, MP4 and the like are all confiscated objects. However, in general prisons, MP3 players with no recording and radio functions are appropriately relaxed, and they can listen to music.