rednet.open("top")
local speaker = peripheral.wrap("bottom")

local function alarm()
    for i = 0, 300, 2 do
        redstone.setAnalogOutput("back", 15)
        speaker.playNote("harp", 3, 4)
        os.sleep(0.5)
        redstone.setAnalogOutput("back", 0)
        os.sleep(0.5)
    end
end

local co = nil

while true do
    local senderId, Message, protocol = rednet.receive("light_42", 300)
    if Message == true then
        redstone.setAnalogOutput("back", 15)
    elseif Message == false or Message == nil then
        redstone.setAnalogOutput("back", 0)
    elseif Message == "alarm" then
        if not co or coroutine.status(co) == "dead" then
            co = coroutine.create(alarm)
            coroutine.resume(co)
        end
    end
    os.sleep(0.1)  -- Add a short delay to prevent constant looping
end