The 88-year-old was targeted in her Ballynasilloe Park home, in the Culmore Road area, on Tuesday at around 11am when someone knocked on her window and she opened her front door.
The woman’s daughter told the ‘Journal’ that her mother thought it was a meal delivery service.
The victim - who has underlying health conditions - was pushed into a room by the intruder who taped her eyes and wrists.
However, she managed to feel for her panic alarm under her clothing and pressed it.
It was on hearing an intercom call from the alarm company asking the woman if she needed assistance that the intruder fled the scene.
He managed to get away with her purse.
The woman’s family is convinced the alarm system frightened the intruder off.
“It saved her life,” said her daughter.
“She always wears it round her neck and she was quick-witted enough to press it while this person was out of the room.”
The daughter believes the emergency devices are essential.
“My message to the public is anyone who needs one must get one.
“We think the government should look into the possibility of funding a scheme for those people who don’t have the resources to purchase such a system.
“We are also asking families to take responsibility for their elderly loved ones and to make sure they wear the alarm. There’s no point hanging it on a hook or putting it away in a drawer. They need to wear it 24/7. What happened this week proves just how important they are. I dread to think what could have happened if mum hadn’t been wearing hers.”
Meanwhile, Foyle MP Colum Eastwood has described Tuesday’s assault on the elderly woman as “disgusting and shocking” and said it had sent “shockwaves through our community”.
“Crime against our elderly community should be taken very seriously and those responsible should face appropriate punishment,” he added.
Mr Eastwood urged older people to take extra security measures and said it was vital people verified the identity of “anyone they do not know before opening the door to them”.
“I would also ask people to keep an eye out for elderly neighbours and regularly check in with them,” he said.
Police are appealing for anyone with information to come forward.
“This must have been a terrifying ordeal for this lady and we are following all lines of enquiry to identify the male involved,” PSNI Det Sgt Connolly said. “While this sort of crime is uncommon, we recognise the impact it will have on older residents in our community who are, perhaps, fearful”.
“There are a number of initiatives which are really helpful, including the ‘No Cold Calling’, the ‘Nominated Neighbour’ scheme, QuickCheck, Neighbourhood Watch and ScamwiseNI Partnership and details of all of these can be found on our website at psni.co.uk.
“I would appeal to anyone who may have witnessed this incident or who may have seen anyone suspicious in the area or who may have dash-cam footage to call detectives on the non-emergency number 101 quoting reference number 510 02/11/21, or to submit a report online using the non-emergency reporting form via http://www.psni.police.uk/makeareport/. “
Crimestoppers can also be contacted anonymously on 0800 555 111 or online.