On the left is the residual current device RCD: the purpose is to detect leakage to ground and disconnect the house thus preventing electric shock. If wire is accidentally touch, the device will trip rather than the person receiving fatal shock.
The yellow replaceable cartridge is the surge protective device SPD: it ensures that appliances in the house does not see voltage spike in excess 385V due to ON/OFF of high surge current devices like compressor, pump etc. It also ensure that lightening surge doesn’t go beyond 1.5kV. These two occurrences, which happens in nanoseconds to microseconds accounts for majority of failure of household appliances, especially electronics. As can be seen, the device has taken many hit from such surges in its 3 months of operation and is deteriorating. When the window completely changes to red (from green), it means it needs replacement.