Muslim scholars have different opinions regarding the announcement of Adhan when one praying alone. Yet, no one can deny the fact that saying Adhan is a good act in itself, regardless of whether it’d be heard by people or not.
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “There is nothing in the Islamic sources that makes it a must for anyone praying alone to call Adhan, for Adhan is an announcement about the upcoming Prayer intended to gather people. Since there is nothing in the sources explicitly making it obligatory, scholars and jurists of Islam have held different views about it. Some scholars consider it recommended. They base their view on the Hadith in Sahih Al-Bukhari, which states, on the authority of Abu Sa`id Al-Khudri, that the Prophet, peace and blessings be on him, told him, “I see you love the sheep and hillside. So if you are with your sheep or on the hillside, and you happen to call Adhan, you should call it loudly; for a muezzin’s voice reaches no one among the species of the jinn and mankind, without he acting as a witness for him on the Day of Resurrection.” Abu Sa`id said, “I heard it (the Hadith) directly from the mouth of the Messenger of Allah.” In his commentary on this Hadith, Imam Ibn Hajar, the great scholar of Hadith, and a jurist, says: “This Hadith shows that it is recommended to call Adhan even if one prays all by himself in a desert, and he expects no one to attend the Salah, for if he were to miss the supplication of other worshippers, he would definitely not miss the testimony of others (i.e. other creatures) who may have heard him.”
On the other hand, there are other scholars who do not consider Adhan necessary when a person is praying alone. This view has been attributed to Imam Ash-Shafi`i. He bases his view on the fact that Adhan is simply a call to let people know about the upcoming Salah.
Having quoted both views, we should conclude by saying that no one should argue over this issue. Since Adhan is a Dhikr, it is good if a person calls it. However, if one does not call it, while praying alone, it is not a sin either, since we can only impose on people what the Lawgiver has imposed; no more, no less.”