Heart Glasses

Heart Glasses outline other players within 24 blocks. Who gets the outline depends on teams (the vanilla /team command):

• If you are on a team, your teammates glow, also through walls. Players outside the team don't glow at all.
• If you have no team, every player glows, but only while there is a clear line of sight between you.

Only you see the outlines, and spectators never get one.

Before 0.3.0 the glasses showed everyone through walls to a player without a team. On a PvP server that was a wallhack, so it went.