TIRED of hearing other people’s cellphone conversations? It may become worse. Soon you may have to watch their favorite television shows and YouTube videos, too, as they project them onto nearby walls or commuter-train seatbacks.

Pint-size digital projectors are in the works. These devices, when plugged into cellphones and portable media players, will let consumers beam video content from their hand-held devices to the closest smooth surface  entertaining themselves, annoying their neighbors and possibly contributing to a new warning sign: No Projectors in This Area. The microprojectors, still in prototype, use light-emitting diodes, lasers or a combination of the two to cast a display of up to 50 or 60 inches, or perhaps even wider, in darkened spaces and 7 to 20 inches or so when there is ambient light.

Digital projectors were once bulky. These new models, though, are small enough to fit into the pocket of consumers who want a big-screen experience from a small-screen device. Some of the models are expected to be on the market by year-end, or sooner.

Prices have yet to be announced. Matthew S. Brennesholtz, an analyst at Insight Media, a marketing research firm in Norwalk, Conn., says he thinks the projectors will initially cost about $350, then quickly drop to less than $300.