hi yusuf
excellent !!
OK, as pommie suggested in post #2 in this thread, you could use a 1k resistor between the output pin (pin3) of the timer and the base of the transistor
it is there to limit current flow through the base of the transistor
You may also need a small value resistor in the collector lead of the transistor as well, that is really dependant on how much current could be supplied by that 3.7V
Your other choice of method would be to use a very small relay to short the keypad connections
cheers
Dave