Hello! I am new. So I might say rather not smart things here. So be patient please 
So I am doing my school project, which is just a gag for my teacher to put us through something. But I still want to do it because of the free points, eh? So it's an alarm. Ima send data and receive data. Very simple. SOMEHOW, ..maybe not somehow. My rather not smart brain could not comprehend how to do anything. So I am here to ask for help. I will also try to add my arduino code here. Please don't forget I am a total beginner before saying prayers to what you will see. So, I press start. It sends "T:8\n". The Arduino gets that, then sends the "SUREOK" to confirm. But before my app can even pick that up or while picking it up, it freezes. Sometimes permanently with no response. Sometimes it comes back with a "Socket closed" and "Broken pipe" error. Thanks for everything yall got for me!
BluetooothSayacDEMO.aia (333.9 KB)
ALARM2.txt (3.9 KB)
i made that all the numbers i can.. it dont work 
thanks tho! i had a "bit" of ideo what that block was but you have made it clear for me!
Be sure to use println() at the end of each message to send from the sending device, to signal end of message.
Only use print() in the middle of a message.
Be sure not to println() in the middle of a message, or you will break it into two short messages and mess up the item count after you split the message in AI2.
Do not rely on timing for this, which is unreliable.
In the AI2 Designer, set the Delimiter attribute of the BlueTooth Client component to 10 to recognize the End of Line character.
Also, return data is not immediately available after sending a request,
you have to start a Clock Timer repeating and watch for its arrival in the Clock Timer event. The repeat rate of the Clock Timer should be faster than the transmission rate in the sending device, to not flood the AI2 buffers.
In your Clock Timer, you should check
Is the BlueTooth Client still Connected?
Is Bytes Available > 0?
IF Bytes Available > 0 THEN
set message var to BT.ReceiveText(-1)
This takes advantage of a special case in the ReceiveText block:
ReceiveText(numberOfBytes)
Receive text from the connected Bluetooth device. If numberOfBytes is less than 0, read until a delimiter byte value is received.
If you are sending multiple data values per message separated by | or comma, have your message split into a local or global variable for inspection before trying to select list items from it. Test if (length of list(split list result) >= expected list length) before doing any select list item operations, to avoid taking a long walk on a short pier. This bulletproofing is necessary in case your sending device sneaks in some commentary messages with the data values.
Some people send temperature and humidity in separate messages with distinctive prefixes like "t:" (for temperature) and "h:" (for humidity).
(That's YAML format.)
The AI2 Charts component can recognize these and graph them. See Bluetooth Client Polling Rate - #12 by ABG
To receive YAML format messages, test if the incoming message contains ':' . If true, split it at ':' into a list variable, and find the prefix in item 1 and the value in item 2.
...
Thank you very much! now i have solved the problem on the App Inverntor side thanks to you it does send the START command. But still i cant get the arduino to start the procedure when it has "START" i know this isnt a problem on this forums side but since you do know things i really wanted to ask it to you too! Thanks for your replies! will leave my things anyway so that you can maybe take a look for me and perhaps help
ALARM2.txt (4.4 KB)
BluetooothSayacDEMO (1).aia (334.4 KB)