into the operating mode or maintained the operating mode in the situation where the first light sensor 13 a is blocked and the second light sensor 13 b is triggered or blocked or where both the first light sensor 13 a and the second light sensor 13 b are triggered and when the cpu 11 has not received an instruction to enter the operating mode for a specific period of time such as 3 to 5 seconds the hand held electronic device 10 will then automatically enter a power saving mode whereby the monitor 15 and a portion of key functions are shut down in order to reduce power consumption if the cpu 11 receives signal before the deadline of the specific time period the hand held electronic device 10 will follow the instruction to enter the operating mode then the operating mode will continue and the specific time period will only start to run from the moment when an ensuing instruction to enter the power saving mode is received referring to fig2 and fig3 which are schematic views of the front side and the back side of the hand held electronic device in the preferred embodiment of the present invention respectively the front side of the hand held electronic device 10 is provided with the first light sensor 13 a the monitor 15 and the key module 17 and the back side of the hand held electronic device 10 is.