I don't know if this is old but i haven't read it elsewhere.

Anyway, the magnetic switch is at the back of the N800. If you take the cover off, you'll find a square magnet right at the center!

If you want to see it in action, try playing a song (which is stored in your non-removable memory slot) in canola, then remove the back cover halfway through.

Yeah, the magnetic switch lets the N800 understand if the battery bay cover is open or closed. The idea is that when you open the bay, a magnet stored on the back of the cover is pulled away from the magnet sensor. The OS registers the change in status and flushes the page file on the internal memory card and then unmounts the card. It will not mount the card unless the cover is on AND THE MAGNET HASN'T TORN LOOSE FROM the cover. On my N800, I had the unfortunate experience of having that magnet disappear due to crappy adhesive. It took me a couple days to figure out and I initially thought my internal memory card slot had gone bad. The magnet needs to be a fairly strong magnet to trip the sensor, too. I fixed mine by canibalizing a magnet from a set of earbud headphones, using a dremel to cut it to the right shape and then using some heavy duty long-curing epoxy to hold it in place. I am kinda pissed that Nokia used such a badly designed mechanism to hold the magnet in place.

You can read the full story on my blog, here:

http://deliverator.silverfir.net/?p=431

THIS thing really technical ..... but i think its pretty KEWL!!!!

There is a similar magnet in 770, too. Opening the back cover seemed to shut down my device after a small delay. I'm running OS2006 from MMC, so I don't know if this behaviour was intentional or caused by unmounting of MMC..

Does anyone have better knowledge what this magnet does in 770 (as there is only one memory card)?

Tragos, as far as I know, the magnet in the 770 was designed primarily to enable power saving mode when the metal slip case was in place.

There are two magnets in 770. One inside the metal case to enable the power save mode and another inside the battery cover (which purpose I do not know).

BTW, there is already a thread about this issue: http://www.internettablettalk.com/fo...ead.php?t=4318

Nothing, really. It wold have disappeared in n800 if it hadn't had the internal slot.
The magnet was supposed to generate an interrupt to detect the removal of the battery cover and perform some emergency action, but the time available in the worst case (device dropped, battery cover _and_ battery popping out immediately) is really nothing. Luckily, jffs2 is designed to cope with such situations and applications are required to never modify live data, only copies so that updates happen atomically.