This project is aimed to design a security locking system by using DTMF technology. Security is prime concern in our day-to-day life. Everyone wants to be as much as secure as to be possible. An access control systems forms a vital link in a security chain. The micro controller based digital lock presented here is an access control system that allows only authorized persons to access a restricted area. This system is best suitable for corporate offices, ATMs and home security. The main idea is to provide security to homes and offices by implementing security system for doors using microcontroller. This project uses DTMF (dual tone multi frequency) technology for opening and closing door. This project is designed in such a way that dc gear motor is interfaced to the controller through driver IC L293D for opening and closing of the door along with the mobile which supports DTMF using DTMF decoder. A normal mobile phone will be used as a remote control on the transmitter side; some keys in mobile will be dedicated for opening and closing of the door. When an authorized person wants to access the door he has to make a call to the mobile on the receiver side from remote mobile. Now the call is being established between the two mobiles. Now any key pressed on the remote mobile will generate a complex frequency, which can be heard on the mobile placed on the receiver side. That frequency can be detected by controller by means of DTMF decoder. Keys assigned for control can be User Defined. The microcontroller will be programmed in such a way that if the received data from the decoder matches with the pre set value then the DC gear motor is operated for a limited time to unlatch the lock so the door can be open. At the end of preset delay, the DC gear motor is operated in reverse direction and the door gets locked again. A 16X2 LCD will be interfaced to the controller on the receiver side to display the status of the door. Buzzer is also interfaced to the controller when the received data from the decoder will not matches with the pre set value then it will be on. This project uses regulated 5V, 500mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/12V step down transformer.