My son has an impression tablet 10 and has forgot the lock pattern. How can we reset it without knowing the code?
If you entered your pattern incorrectly 5 times, Android would lock the lock screen so you cannot draw any more pattern for 30 second (this is to prevent brute forcing) and a button will show up that will allow you to reset the pattern by entering your Google Account email and password.
The image on the left is what the lock screen normally looks, after entering the pattern incorrectly 5 times, another button appear on the bottom.
You may be able to figure out the lock pattern by looking at the phone screen in the right light, or taking a picture and perhaps performing simple contrast adjustments on the picture. See “Smudge Attacks on Smartphone Touch Screens” by Aviv et al (presented at WOOT 2010).
Unfortunately you're probably going to have to do a factory reset, which will wipe all the data on the device (it should leave the SD card alone if there is one, though).
You may be able to do this from recovery mode, which you get into by holding some of the buttons on the device while it boots up. I don't know what buttons the devices has though.
Another method is to install the Android SDK and the tablet's drivers on your computer, connect the device, and do something like the following from a command prompt (the path may vary):
cd C:\Program Files\Android\android-sdk\platform-tools adb shell wipe data
Edit: From looking online it appears that there is no button combination to get into recovery, though
adb reboot recovery might work. If you're going to install the SDK though you might as well just use the wipe command I posted above.
On my Motorola Cliq (an older phone), I was able to reinstall the firmware, and my phone became completely unlocked. It erased some of my system settings, but all of my apps, data, and files on the device were still there.
As a test, I also re-flashed my newer phone (LG Motion 4G, Android 4 ICS) and it kept the password lock. Though, my guess would be that I could probably find a way to erase the password with a specially crafted update.zip file.
(Here is a link of someone who created an update.zip to erase the pin and gesture password in Gingerbread, and it looks like it would work for my ICS phone too).
If this makes some people paranoid, then the lesson here is to setup an app which allows you to remotely erase all your data. A knowledgeable person with physical possession of a device will not be stopped by the presence of a password.