From Best Brass in Japan, a diminutive practice mute that amplifies your sound through the included earphones.
e-Brass reduces instrument output to a whisper, lowering volume approximately -30dB to -35dB. With its amazing quietness, you don't have to worry about disturbing the neighbors and also can enjoy playing the instrument without feeling self-conscious about other people listening. Using the e-Brass is just like playing in a completely portable and personal studio where nobody can bother you.(*)
* Even so, please be conscious of your circumstances...