@giebek could you describe the problem, what your setup looks like, and what you have tried so far to troubleshoot it? There are 137 posts in this thread so it is a bit hard to figure out which problem you are referring to.

@sharpy if the node is battery powered, NO or NC can make a big difference. Which one is best depends on if the door is usually open or closed.

Yes, with two NC in series you could detect that one of the doors is open. You would not know which door though, and if one of the doors was left opened you would not be able to detect if the other door is open or closed.

Welcome to the MySensors forum @talhayounis

Th best way to get started with MySensors is to first read the getting started guide. Then you can move on to https://www.mysensors.org/build/gas which has an example sketch to use with MQ135 and MQ7.

The best way is usually to get a gateway and a simple node running, and then expand from that.

@alowhum done

@tekka I see. Thanks for explaining.

I thought the bootloader is overwritten when using ISP? So "you don't need a bootlader" is slightly incorrect, you can not have a bootloader when using isp?

@fernando-alvarez-buylla the link (created with the ln command) will be removed at reboot. Change my-serial-pty=/dev/ttyMySensorsGateway to my-serial-pty=/dev/ttyUSB020 and re-run all the commands.

If you don't reboot the pi after enabling the mysgw service, you will need to start the gateway as per the instructions printed when make is finished.

@encrypt yes they look good

Nice work @encrypt

Does the gateway startup CP=... line match the settings for the node?

@bgunnarb there is no way for the rpi gw to affect your ability to use ssh, so the problem is probably on the network or OS level.
Does dmesg or syslog say anything around the times when the problem occurs?