A speaker cone displayed with one sound wave, generally used as an icon to indicate the decreasing of volume on a phone or computer.
Previously displayed with two sound waves on Android, instead of one.
Speaker Medium Volume was approved as part of Unicode 6.0 in 2010 under the name “Speaker with One Sound Wave” and added to Emoji 1.0 in 2015.
U+1F509
? Speaker with one sound wave