When I start the TX the first data that comes to the rx is around 5000 feet. I then push a button on the TX arduino board and the data is set to the height that I am at as 0 feet. I have loaded your code and the Oled shows 5000 feet and the buzzer just buzzes as set in the code. When I push the button on the TX the height on the tx goes to 0 but the rx is still stuck in a loop and shows 5000 feet on the Oled.The buzzer should not be on but it does buzz. If I may repeat perhaps more clearly what I am trying to achieve.
When the Oled shows 100 feet the buzzer should only buzz once every say 2 seconds, if the height is 200 feet then twice very 2 seconds and so non until it buzzes 8 times every 2 seconds at 800 feet. After every buzzer sequence of 2 seconds the code should check whether 200 feet has been reached and not stick in the loop. There should be no buzzer until 100 feet is reached. I hope this is clearer now, did you misunderstand me?