What is SIMLock? SIMLock, or simlockd, is a small application written for the Nokia N900 that provides the ability for your phone to automatically lock itself if it detects that the SIM card has been changed. This is done using the phone's built in lock functionality and only requires that you have set a lock code on your phone. What does SIMLock do? When your phone is started up after installing SIMLock your current SIM Card's unique identifier, known as an IMSI, is stored. Each time the phone is started after that the current SIM Card's IMSI is compared to the original one. Should SIMLock find that your SIM Card's IMSI is different it will automatically lock the phone and put it into Offline Mode. Once the phone has been unlocked again SIMLock will add the current SIM Card's IMSI to the list of "allowed" IMSI numbers and it will not bother you again. Why should I use SIMLock? SIMLock provides an added level of security should your cellphone be stolen. While not being completely bulletproof the aim is to make it just that much more difficult for a thief to use your phone after he has stolen it. It is written to behave similarly to the functionality available in the Symbian UIQ phones of late and seems to function very well. Where can I get it? SIMLock is available for download here and information about the changes made to it can be found on this page. I found a bug! If you have managed to find a bug please feel free to send information about what happened to me at contact@sierrasoftworks.com or if you want to try your hand at fixing the problem yourself you can grab the source code from http://gitorious.org/simlockd. Download Changes Source Code