The present perfect tense denotes an action beginning at some time in the past and continuing up to the present moment.

It is formed using has or have before the past participle form of the verb.

Has is used before a singular subject and have with a plural subject.

In a short period of time, cellular technology has transformed people's way of communicating with each other.

People have found a way of getting in touch even when they are traveling on land, water, or air.

The negative form has not between has/have and the past participle of the main verb.

People's life has not been the same ever since mobile phones were introduced.

Time expressions related to the present perfect tense are since last year, ever since, for a month, already, just, for some time, for a week, etc.

When the sentence is in the passive voice, has been or have been is used before the past participle form of the verb. In the active voice, has or have is used.

Passive Voice:

Mobile phones have been used by pupils in schools for years now.

Many business people have been led by necessity to have several mobile phones at a time.

Active Voice:

Pupils have used mobile phones in schools for years now.

Necessity has led many business people to have several mobile phones at a time.