Al-Bukhaari (570) and Muslim (681) narrated from Abu Qataadah (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) was with some of his companions on a journey, and they halted at the end of the night. He lay down his head, then he said: “Guard our prayer for us.” The first one to wake up was the Messenger of Allaah (peace and blessings of Allaah be upon him). When the sun was on his back. We woke up, startled, then he said, “Ride on.” So we rode on and traveled until the sun had risen, then he stopped and called for the water vessel I had with me, in which there was a little water. He did wudoo’ from it, using less water than usual. A little water was left in it, and he said to Abu Qataadah, “Guard your water vessel, for you will see something happen with it.” Then Bilaal gave the call to prayer and the Messenger of Allaah (peace and blessings of Allaah be upon him) prayed two rak’ahs, then he prayed Fajr, and did as he did every day. The Messenger of Allaah (peace and blessings of Allaah be upon him) rode on and we rode with him, and we began to whisper to one another, saying: What expiation is there for what we have done by neglecting our prayer? Then he said: “Do you not have an example in me?” Then he said: “There is no negligence in sleep, rather negligence is the fault of one who does not pray until the time for the next prayer comes. Whoever does that, let him pray when he remembers it, and if it is the following day, then let him pray at the time of the prayer (that he missed).”
The above states that missing salah because of sleep is not a sin.
Al-Nawawi said in Sharh Muslim (5/186):
This is evidence for that on which the scholars are unanimously agreed, that the sleeper is not accountable.
However, nowadays we've got alarms to wake us up. If one has an alarm, they should use it to wake themselves up to pray salah and wouldn't the one who ignores using the alarm is guilty of being ignorant?
Question: Is it a sin to miss salah because of sleep nowadays?