Cockroaches are predominantly nocturnal by nature and spend the day hiding in cracks and crevices around areas like sinks, drains, cookers, kitchen cupboards and the backs fridges and other electrical items. They may be seen scurrying away if you come home at night or during darker days and put the lights on. 

In cases of severe infestations, cockroaches emit a foul smell often likened to an almond like smell. This is especially true in the case of german cockroaches in very high levels of infestations.