We're all familiar with the concept of using dogs to help the blind, but what is not so widely known is that they also help the deaf. Women's editor Sarah Foster meets Averil Collinge, whose hearing dog is well and truly her best friend.

IT is a well-rehearsed routine, but no less watchable for that. As placid Tulla, a two-and-a-half-year-old retriever cross, lies gently dozing in the sun, her guardian Averil Collinge goes to set her cooker timer. There is a pause of several minutes and then the bleep of an alarm, which pretty soon, has Tulla pacing round and round. Once she's identified the sound, she puts a paw on Averil's lap - and then it's Averil's turn to act.

She makes a show of standing up, demanding urgently "What is it?", then Tulla leads her to the sound. Once she has switched off the alarm, it's time for Averil to give praise, and as she hands out doggy treats, it's clear that Tulla is in heaven. The demonstration now complete, she trots off happily for her bone.

Although she is a working dog, when Tulla's not on duty, she seems like any other pet. She lives with Averil at her home just outside Harrogate, and when a visitor comes to call, she bounds to lick them half to death. She is a sunny-natured creature with golden hair and gentle eyes - the sort that anyone would take to - and yet her easygoing outlook masks her dreadful start in life. Like many other hearing dogs, she was abandoned by her owners.

"It took quite a time to bond because she'd had a very chequered life," says 81-year-old Averil. "She was dumped in Ireland and the people who found this puppy took her to the equivalent of the RSPCA, who periodically contact Hearing Dogs for Deaf People and say 'I think we have got some dogs that might be suitable'. They went over and decided Tulla would be trainable and brought her back."

The largest charity in the world that works within the specialist field, Hearing Dogs for Deaf People has now been going for 25 years. With one in seven of the population having significant hearing problems, it feels the dogs that it provides are an invaluable resource. There is no charge to the recipient, although they have to be assessed, and they can choose the size of dog to suit their individual needs. In Averil's case, as she was used to larger breeds, she thought she'd stick with what she knew. "I've always had big dogs," she says. "They instinctively helped me; it's in a dog to respond to sounds."

Averil blames her hearing problems on what she did when she was young. As an employee of an airline, she believes the noise caused lasting damage. "It started about 32 or 33 years ago," she says of her deafness. "I worked for South African Airways as a ground hostess, meeting the aircraft and booking people in, and the Viscount had a very high-pitched whine. Of course, you didn't wear earmuffs in those days - I'm going back to the 50s - and ten or 12 years later I started experiencing hearing loss. The consultant said there was a lot of deafness from that aircraft."

When Averil's husband was alive, she could work round her lack of hearing, but when he died, she realised how much he had helped her. "My husband died 33 years ago now and I didn't realise how much he was filling in for me - he probably said 'the bell's ringing. There's somebody at the door', and so on, and suddenly, I was aware that I wasn't hearing these things," she says.

Averil bought the house she currently owns and started living with her brother, but when he also passed away, her isolation just increased. "The day after the funeral, I came back into the house and I had a dog and I said 'it's just thee and me, doggy', and she died the next night - she had cancer," says Averil. "So, suddenly, with no dog I was bereft."

Averil had previously heard of Hearing Dogs, which has a centre in North Yorkshire and one in Buckinghamshire, and hoped it might be able to help. It was a tough and lengthy process but in the end, she took home Tulla. "They came to assess me and could see that they could help me, and when it was decided that I could be a recipient of a hearing dog, I went to the centre at Cliffe, near Selby, to meet Tulla," says Averil. "I spent five days in residence and the trainer brings the dog over to see whether you like them, then they work with you, showing you how they react to all the bells. Tulla stayed with me for five days as I learned how to handle her, then she came home with me."

A crucial part of Hearing Dogs is the support that it provides, with trainers making frequent visits to check that all is going well.

Now, having been in post a year, it's time for Tulla's last assessment. "Two trainers come over and spend the whole day with me - they don't really know Tulla or me - and they see her going through all her work schedules," says Averil. "If she doesn't pass, I will be heartbroken - but they give you all the backing they can."

It's clear from seeing them together that she and Tulla are inseparable. As well as helping in the home, the dog has duties far beyond it. "If it's a smoke alarm, instead of leading me to the sound, she drops flat onto the floor and I know then that it's a danger signal, and it's the same if we're in Sainsbury's and their fire alarm goes off," says Averil. "She can go everywhere with me because she's an assistance dog. I take her to the supermarket, she's been to the theatre and she's been on a bus. She hasn't been on a train yet, but she's quite happy in the car behind the dog guard."

As she does not belong to Averil but to the charity, it isn't clear when Tulla's residence will be up. If she's successful in the test, it isn't likely to be soon. "She's never my dog, she always belongs to Hearing Dogs, and if they decide she's not working correctly for me, or if she was ill, then they would have to decide what to do - whether I would be given another dog or whether she would stay with me but not as a working dog," says Averil.

For now at least, the odds are stacked in Tulla's favour. To mark the 25th anniversary, a competition has been launched, and having overcome her past to prove a valuable companion, Tulla's in the running to be named the Hero Hound. As far as Averil is concerned, there couldn't be a better winner. "Now that I have her, I'm more secure and certainly not lonely - there's always a dog in the house or with me," she says. "She's a great companion and I'd be lost without her."

* For more information on Hearing Dogs for Deaf People, ring 01844-348100 (voice and minicom) or visit www.hearingdogs.org.uk

To vote for the Hero Hound, visit the website or write to Hero Hounds, Hearing Dogs for Deaf People, Freepost (SCE 14567) Princes Risborough, HP27 9BR