Choice of phone
The important thing when choosing phone for this project is that the phone should
be automatically turned on when a charger is connected. The Sony Ericsson X10
mini has this important feature. It is also a rather small phone which makes it
easy to hide in a car and at the time of this writing a used such phone can
be bought for about 50 €.
Depending on your firmware version, the phone might seem as if it is only
charging and not turned on when the charger is connected. However, the hardware
in the X10 mini is really powered up, but some firmware versions interrupt the
init process to only show a charging icon. This can be fixed, no need to worry.
Rooting the phone
Root privileges are needed to modify the firmware to complete the init process
when the charger is connected. The app to power down the phone when the charger
is disconnected will also need root privileges. To root the phone I followed
the steps described at
Even though that page is written for X10 mini pro the steps worked also on my
X10 mini and the steps worked fine on my laptop running Slackware Linux 12.2.
However, one of the steps described on that page, "touch testfile" did not work
on my phone. The touch program only gave "permission denied" even though I did
have write access as a normal user to that directory.
Complete boot when charging
If your phone only gets one of those ugly battery symbols when a charger is
connected to a powered off phone this is because the init process is interrupted
by /system/bin/chargemon. That file is a binary ARM program, I replaced it with
a simple script containing only a single line:
The file was created and installed with the following steps:
echo "echo skipping chargemon" > chargemon.script
adb pull /system/bin/chargemon chargemon.backup
adb push chargemon.script /sqlite_stmt_journals
$ cd /sqlite_stmt_journals
# mount -o remount,rw /dev/block/mtdblock0 /system
# cat chargemon.script > /system/bin/chargemon
# chmod 755 /system/bin/chargemon
# reboot -p
- When the command su is given above, it might have to be
acknowledged in a dialog on the phone screen.
- The final command reboot -p shuts down the phone. As the USB cable
is still connected it will power on again, and if everything has gone fine
the phone will complete its boot process without halting with any battery
Choice of carrier
For this purpose I choose a prepaid plan from Comviq. Whenever the plan is
refilled with 169 SEK (about 17 €) a data plan with up to 200 MB will be
included for the next month.