You shouldn't get the "your key is still in the ignition" alarm if you turn it back to "On" after killing the engine. I've been EOCing into my parking space every morning lately.
I'll try it again some time (likely going into the parking space), just to make sure.
However, if I'm not mistaking, I tried that experiment before, and it didn't silence the alarm in my car. As far as I can tell, in my car once the alarm goes on, simply putting the switch to "on" doesn't silence the alarm. Instead, you either have to either: A) Phyiscially remove the key and reinsert it. or B) Fully start the engine (not just turning the key to "on").
"I used to think the fuel cutoff threshold was around 1000 RPMs"
According to the service manual (pg 11-29), DFCO for the VX is 850 rpm. For other models, it varies from 870-930. This is for the '92-'95 Civic.
I've verified this by observation, with a meter that monitors the injectors. But I haven't checked to see what happens with a cold engine.
Trivia fans might be interested in knowing that the VX also has fuel cut-off at 113 mph.
On the subject of coasting in gear: I think it's a waste, unless it's your intention to slow down. Think about it this way. If I coast in neutral, I'm using just enough fuel to make the engine spin at idle speed (in my car that's 600 rpm, assuming accessories are turned off). If I coast in gear, I'm using a portion of my momentum to make the engine spin at some higher speed, perhaps 1500-2000 or more. It seems inevitable that this consumes more energy than making my engine spin at 600 rpm. So unless I actually have a need to slow down, and assuming I'm not going to use EOC, then I'm better off consuming fuel to spin the engine at 600 rpm, as compared with consuming vehicle momentum to spin the engine at 1500. The fuel and the momentum are both energy, just in different forms. Conserving momentum is just as important as conserving fuel.
luckily my commute tends to be in the opposite direction of traffic, so i usually dont end up in bumper-bumper jams, but i would like to try this if i do. I was fortunate to hit some bad traffic right at the crest of a really long hill a few weeks ago, and was able to keep my engine off for the duration. Roughly 10mins and 1.2 miles, plus i was able to bump start at the end... I need a scanguage, just to entertain myself at least.