I'm not sure how long after shutting off an i3 with an OBD dongle plugged in that the alarm sounds. Hawaiʻi ran a pilot program to learn how feasible basing annual registration fees on distance driven might be. I joined this pilot program which involved leaving an OBD to cellular adapter plugged in. This adapter would send odometer readings periodically (monthly?) to the pilot program administrator. I told the administrator that leaving an OBD dongle plugged in would trigger an i3's burglar alarm. I was told that they were aware of this and had worked around it. I never heard the alarm, but I was notified that the alarm had been triggered during the night, more than a fews seconds after I had shut off our i3. I told the administrator that I could disable the OBD alarm via coding but that they should not expect all i3 owners to do that and that doing so could be a security risk. I was given the option of sending a photo of my odometer to the administrator monthly.
The alarm shouldn't be triggered while an i3 is on.
Some OBD scanners can display live sensor readings. However, I can't think of any sensors other than some REx engine sensors that provide live data. It seems that mi3 and eFlow poll for a datum and wait until that datum is returned before polling for the next datum, so a driver would be pretty distracted watching the app slowly display updated data over and over. Doesn't seem too useful although maybe others have a different experience.