Their new lifestyle has saved more than enough energy to cover their car's nightly recharge.

The Sabos, who are now coaching some of their neighbors about trimming energy costs, are big fans of the new transparency in energy consumption. But AARP and other consumer advocates say there's a potential downside: higher costs to offset the meter installations and higher electricity prices during peak hours — when many retired or homebound people rely on power.

The California Public Utilities Commission (CPUC) says the time-of-day rates will be optional, but consumer advocates fear they will become mandatory.

"What concerns us is forcing consumers into time-based pricing schemes where seniors and disabled consumers will end up paying more simply because they do not have the option of moving their energy consumption to off-peak hours," said Casey Young, AARP California associate state director for advocacy. "We will be fighting to make sure that consumers are not mandated or defaulted into these pricing schemes."

Mindy Spatt, spokeswoman for The Utility Reform Network (TURN), which has sharply criticized the smart meter rollout in California, said time-of-day pricing will mean "some consumers will benefit, but others will see higher bills, and we don't think that is fair."

Smart meters allow utilities to track power usage in homes and commercial buildings through cellphone-like radio signals. They are gradually replacing conventional electric meters and the workers who read them. California's three biggest utilities — Pacific Gas and Electric, Southern California Edison and San Diego Gas & Electric — expect to have nearly 17 million electric and natural gas smart meters installed by 2012, serving almost all their customers.

Consumer advocates also are concerned that the meters will make it easier for utilities to cut off power for late payments. In the past, someone from a utility knocked at the door before disconnecting a meter.