While a lock screen is great for keeping most people out if a dedicated thief wants to get into it, then they will. While there are many ways to get past a lockscreen, some are wilder than other and this was proven by researchers who beat the Android security on a Galaxy Nexus when they put it in the freezer.
This has been something that has been used in hacking for many years and is known as sol booting. RAM holds on to pieces of data for a short period of time and hackers are able to boot devices into an operating system if the device is turned on and off quick enough. This is where the freezer part comes into it.
When putting the Galaxy Nexus into a freezer the researchers at Erlanger University found out that the RAM could keep data for around 5 or 6 seconds, as opposed to just two. This was enough time for them to shut off the device and then book it back up into fastboot mode. This meant they could steal data from the RAM using a special tool called FROST. They could then use this data to get past the lockscreen, which gave them full access to the device.
However there are some requirements needed to make such an attack. The device needs a removable battery so that it can be closed down fast. It also needs to come with a boot loader that is unlocked. Thieves therefore would need extended physical access to the device. If the device doesn’t meet this criterion, you may still take this as a reminder not to rely on the lock screen for total security as there are generally ways around it.