Stereo

A stereo is an object found in all four Sims games. Stereos range from inexpensive "boom box" units to expensive "audiophile" systems. A stereo provides fun for Sims, and Sims can dance with each other to meet their social needs. In all games, Sims will wake up if there is a stereo playing music in the same room, unless they have the heavy sleeper trait.

In The Sims: House Party, The Sims: Superstar, The Sims 2, and The Sims 4, speakers are available in Buy mode. Speakers allow a stereo to be heard in other rooms, or other parts of the lot.

The Sims
In House Party and Superstar, speakers are 1x1 "stacks" which are placed on a floor or on level terrain. By default, they are turned off, and the player can click on each "stack" to turn it on or off.

The Sims 2
In The Sims 2, Sims can work out in front of stereos, which improves the body skill. Sims can "Listen to Music" while relaxing in bed, if a stereo is in the same room.

A bug introduced in Bon Voyage causes Sims to start dancing on the spot when they are instructed to dance near a stereo, even if they are not in the same room as the stereo. A mod by Cyjon fixes this behavior.

Speakers
In The Sims 2, speakers are wall-mounted, and are always on.

Neukum System Wall Speaker is the only speaker that is available for purchase in community and residential lots. They extend the music from the playing stereo onto rooms they're present in.

Speakers that are exclusive for community lots play only one radio station. Players cannot change the station it plays and Sims cannot be told to dance near it. The station the speaker plays can be identified by the speaker's color and by its name.

In Bon Voyage, vacation locals can do the hula or slap dance near a community lot speaker autonomously.

The Sims 3
In The Sims 3, some stereos improve the athletic skill, but the Showtime stereos don't. Unlike previous games, Sims no longer need to walk near the stereo to turn it on or off, or to change stations; all such interactions occur instantaneously. In addition, players can now control the volume of stereos. A stereo provides the "Enjoying Music" moodlet; on normal stereos, this is +20 with a +10 bonus on certain Sims if it is playing their favorite music genre.

In The Sims 3, a Sim with high Handiness skill can perform the upgrade Wire House With Speakers, which causes the "Enjoying Music" moodlet to follow Sims around the house and likewise prevent them from sleeping (unless they have the Heavy Sleeper trait). Unlike the Buy mode speakers in earlier games, this upgrade affects the entire house; the player cannot choose which rooms will have speakers.