That the saints in heaven are somehow made aware of our prayers is indicated in Revelation 5:8, where the twenty-four elders in heaven are described as having bowls of incense that is the prayers of the saints.
Something else to consider is that the soul of dead Tabitha did not seem to have any problem hearing St Peter when with faith he said to her, “Tabitha, rise.” (Acts 9:40)
One of the possible ways the saints in heaven might be made aware of our prayers to them is via angels acting as prayer messengers. The Bible fairly regularly describes angels as delivering messages from heaven. However, Jacob’s vision of the ladder not only had angels descending from heaven to earth but also had angels ascending from earth to heaven. (Genesis 28:12) So, perhaps angels also take messages to heaven. In fact, in Tobit 12:12-15, the angel Raphael says he presented the prayers of Tobit and Sarah in heaven. And, in Revelation 8:3-4, an other angel is described as presenting the prayers of the saints before the throne of God.
Angels acting as prayer messengers not only seems biblically sound but also answers the question, How can one saint in heaven possibly hear the simultaneous prayers of numerous people from all over the world since only God is omniscient and omnipresent? The Bible, in Matthew 18:10, suggests that each of us, or at least each believer, has an angel assigned to him. Perhaps when we finish praying, our assigned angel zips up to heaven and presents our prayer to the heaven court, to God or to one or more of his saints, and then zips back down to us. In that case, all that is necessary for a saint to be made aware of the simultaneous prayers of numerous people from all over the world is for all those angelic prayer messengers to figure out a way to present the prayers of their charges to the saint in an orderly and expeditious manner.