Young Chinese salesman Xiao Li has developed a fear of his mobile phone. Because of the nature of his work, he always keeps his mobile phone on-hand so he can immediately answer calls from clients and his company.

"Often, I think I hear my mobile phone ringing, but when I look, there never was any call or message," he said.

He even thinks he hears it faintly ringing when the power's off.

Xiao's doctor has diagnosed him with acousma - an auditory hallucination that causes people to imagine they hear a particular sound.

Acousma also plagues some young Chinese who use QQ, a popular online messenger service, which beeps when users receive an incoming message.

Doctors believe that it is a psychological problem caused by strong dependence on mobile phones or QQ. Upon hearing the sound of his mobile ringing, Li must whip himself into "work mode". He has been on standby for so long now that it is beginning to affect his psyche.

Researchers believe that people with certain professions in which mobile phones are used frequently, such as sales, consulting and media, are at greater risk for acousma.

About 50 percent of the population suffers from some form of mental illness, such as anxiety and depression.

And anyone could experience short-term hallucinations and delusions. So, doctors are inclined to believe that because most people with acousma only have the condition temporarily, it doesn't affect the normalcy of their lives and isn't a mental illness.

Only when the hallucination becomes longstanding and convincingly real does acousma become a mental illness. Serious audio hallucinations are a symptom of schizophrenia. So, in that case, people with acousma should seek help from a psychiatrist.

"Find a suitable day to turn off your mobile phone and completely relax," Li's doctor told him.

The doctor also suggested occasionally changing his mobile ring tone and using slower, more relaxing music.

It is believed that acousma is caused by work pressure. It is suggested that people who hear imaginary mobile rings should weigh the intensity of the pressure they face and consider whether it negatively influences their lives. It is advised that people adjust their work schedule and lifestyle to alleviate stress or even consider changing their lines of work.

Five typical symptoms of mobile acousma:

*You worry your mobile will ring and check it every half hour;

*There is no incoming call, but you can "hear" your phone ring;

*Wherever your mobile is, you think it is ringing or vibrating;

*You become so nervous when there is a call that your heartbeat quickens;

*You get a new mobile phone but still hear the ring tone of your old mobile.