An Australian woman lost for three days in dense bushland has been found after a man remotely monitoring security footage saw an 'SOS' sign scrawled in the earth on his property.

Deborah Pilgrim went missing on Sunday while camping with friends about 100km from the South Australian state capital of Adelaide.

The 55-year-old took a walk from the campsite and lost her way.

Dozens of police and emergency services personnel, as well as a rescue helicopter, were called in to search the remote area, but after three days had failed to locate the missing woman.

Late last night a man remotely monitoring CCTV footage of his property near the South Australian search area, noticed an SOS sign etched into a dirt driveway near his unoccupied home.

He alerted police, who found Ms Pilgrim close to midnight on a neighbouring property where she had located water.

"It was so overwhelming," an exhausted Ms Pilgrim said.

"I think I dropped to the ground," she added, recalling the moment rescuers arrived.

Neil Marriot, whose CCTV cameras had picked up Ms Pilgrim's distress signal, said he had only recently had the security system installed after several recent break-ins.

"I'm so pleased she was able to find water because I feared the worst for her - I really did," he said.