MALIBU, Calif. — The battle between Malibu beachfront homeowners and a less privileged public that wants to share the stunning coastline has been fought with padlocks, gates, menacing signs, security guards, lawsuits and bulldozers. There seems little question who is winning: 20 of the 27 miles of Malibu coastline are inaccessible to the public.

Yet this month, the homeowners — including some of the wealthiest and most famous people in the country, but also a hearty colony of surfers, stoners and old-fashioned beach lovers — are confronting what may be the biggest threat to their privacy yet.

The smartphone.

Jenny Price, an environmental writer who has pressed the battle to open hidden beaches, has developed an iPhone app offering a beach-by-beach battle plan for anyone wishing to explore what are, by design, some of the most secluded beaches around. It has maps to often hidden entry gates, house-by-house descriptions showing public property boundaries and spine-stiffening advice on dealing with counterfeit no-parking signs (“feel free to enjoy and then ignore”) and threatening property owners (“they’re welcome to call the sheriff”).