The first transistor radio, the Regency TR-1, was introduced in 1954. It cost $49.95 (the equivalent of $334 in year-2003 dollars).
The use of transistors instead of vacuum tubes as the amplifier elements meant that the device was much smaller and required far less power to operate. The typical "portable radio" of the fifties was about the size and weight of a small laptop computer, and contained several heavy (and non-rechargeable) batteries: one or more "A" batteries to heat the tube filaments and a large 45 to 90 volt "B" battery for plate voltage. By comparison, the "transistor" was about the size and weight of today's cassette-playing Walkman and operated off a single 9V battery.
Transistor radios did not become popular until the early sixties, when costs came down. Although usually equipped with headphone jacks, the most common way listeners used them to them was to hold the entire radio directly against the side of the head, with the speaker against the ear. These radios, of course, were monaural and limited to the FM band. Holding the radio to the ear minimized the irritatingly "tinny" sound, commonly attributed to their tiny speakers, but equally due to the use of inadequate coupling capacitors.
The transistor radio remains the single most popular and prevalent communications device in existence. Some estimates hold that there are at least seven billion of them in existence, almost all tunable to the common AM band, and an increasingly high percentage of those also tunable to the FM band. Some get shortwave service as well. Most operate on battery power. They have become increasingly small and cheap due to improved electronics which pack millions of transistors on one integrated circuit or "chip". The prefix "transistor" basically now means an old or cheap radio.
The ability to set up low power radio stations for community radio and pirate radio has also promised to breathe new life into the older radios and bands.
See also: broadcasting