The idea that someone who talks about suicide won't actually go through with it is a myth. The majority of people who have committed suicide gave some kind of advanced indication of their intent. Though it's true that many people succeed in ending their own lives every year, the majority of suicides can be prevented if we know the signs to look for.
The person may verbally express the desire to end his/her life, by stating a wish to be dead or wanting to die, or saying things like, "It would be better if I wasn't here."
The person may exhibit or express extreme feelings of loneliness, worthlessness, hopelessness, and helplessness.
The person may exhibit changes in personality such as withdrawn behavior, irritability, pessimism, apathy, anxiety, or panic.
The person may have experienced a recent major loss such as the loss of a job, or loss of a loved one as the result of death, divorce, separation, etc.
The person may have made earlier suicide attempts or may have had another family member who committed suicide in the past.
The person may have a history of psychiatric illness, depression, or alcoholism.
Person may appear to have a 'death wish', and may exhibit incautious behavior that could lead to death such as reckless driving.
The person may exhibit a desire to tie up loose ends, by taking care of personal affairs, visiting old friends, writing a will, etc.
The person may suddenly switch from being sad to being very calm and happy.
All of these signs should be taken very seriously and dealt with immediately. Do not leave the suicidal person alone. Contact a doctor, suicide prevention or mental health facility right away.