renault clio?

hey a resently bougth a renault clio second hand (1999) . aye only got 1 key with the car and was going to get another cut . after lookin on sites av have realised my car is a ment to half central lockin but this dose no work as aye need to do it manually any body got any ideaz how to fix this ? aye have shaken the key and you can hear a rattlen sound comen from inside the key :O