Each Sing-a-ma-jig is battery-powered, with two AAA batteries already included. They are soft, plush dolls with terrycloth mouths, and measure about 12 inches in length.
The dolls make a variety of different noises when squeezed. Each "squeeze" causes the Sing-a-ma-jig to open its mouth to emit noise. The doll's mouth contains a set of plastic teeth that click together when closing. A Sing-a-ma-jig's noises include songs, "jibber-jabber" made up of vowel sounds, different notes on the octave scale, a greeting, and occasionally a goodbye. They each sing a different public-domain song unique to their model. The voice that each one has is unique to its model as well.