On October 7th how did the prayer 'Shema' save Jewish lives?

How did Israelis know when the IDF actually showed up on October 7th? When a voice rang out to them, while they hid in their bomb shelter, what made them belief it was another Jew, an IDF soldier who had come to save them? Hear how creatively Israelis used the most important prayer in Jewish liturgy to send a sign of authenticity to one another.