Suicide and other damaging behavior towards oneself or others are very similar to just about any medical disorder.
This is because it does not happen at once and is usually preceded by emotional turmoil such as agitation, anxiety, feelings of hopelessness or helplessness and impulsivity.
Other people will notice the change in terms of his or her performance at work or in school as well as the actions done at home.
If the person enjoys hanging out with friends and then shuts them away, these are just signs that things will get worse.
Some of the warning signs of destructive behavior other than killing oneself are agitated behavior, giving away money and properties, overdosing, verbalizing death and wrist slashing.
If you know of someone who is contemplating on doing it, instead of doing nothing, the best thing to do is to reach out and talk to that person.
Chances are they will be encouraged to express their feelings.
Simply asking if there is a problem and then clarifying if that person has entertained any destructive thoughts may be all it takes to save a life.
If you are able to reach out, such a deed does two things.
First, it shows you are concerned about that person's welfare and second, it helps the individual acknowledge that a problem exists and there is an urgent need to address it.
When you make yourself available to that person, you are reassuring them that no matter what, you are there.
If you need assistance, you should get professional help by calling the police or the mental health services in your area.