TORONTO - If you remembered to set your clocks back one hour Saturday night, officials say your work isn't done yet-- you need to change batteries in several life-saving devices too.

Most of Canada returned to standard time at 2 a.m. Sunday morning.

Health Canada is warning those who rely on medical devices with internal clocks to check them for the time change.

Implanted pacemakers/defibrillators, Holter heartbeat monitors and glucose level monitors made before 2007 could be affected.

Fire officials are reminding people to change the batteries in their smoke and carbon monoxide detectors.

They say fresh batteries will give homeowners critical extra time to escape.

And insurance companies are warning drivers that the time change can affect their reaction times.

Meanwhile, Apple says the end of daylight savings time could cause problems for iPhone or iPod touch users.

The company said it will release a software update because alarms on those devices may not recognize the end of daylight saving time.