BC847 is an NPN transistor so when no power is applied to the base, the collector and emitter will be left open (Reverse biased) and when a positive voltage is applied to the base pin, the transistor will turn on.
The BC547 is an SMD SOT23-3 package NPN Transistor with VCE of 45V and a collector current of 100mA. It can be used as a small signal switching transistor. It also has a low base voltage of 6V.