Luckily for Brazil, it is in the middle of the South African plate and not on the edges of any tectonic plates. This means that they do not have many volcanoes there at all (http://www.invivo.fiocruz.br/ cgi/cgilua.exe/sys/start.htm?UserActiveTemplate=english &infoid= 1275&sid=43). Although they do have some. On the Brazilian island, Trindade, there is a volcano which classifies as dormant (https://www.volcanodiscovery.com/trindade.html). A dormant volcano is a volcano that has not erupted in the past 10,000 years, but is still expected to erupt again. There are no active or even dormant volcanoes on mainland Brazil, but there are two extinct volcanoes in the mainland. There is the Nova Iguaçu Volcano and the Pico do Cabugi Volcano, both in the mainland and extinct (https://en.wikipedia.org/wiki/List_of_volcanoes_in_Brazil). An extinct volcano is a volcano that no one expects to ever erupt again.
I could not find anything on what Brazil is doing to warn people when a volcano erupts, and I imagine that this is because there are two volcanoes that are mainland and they are both extinct. The closest volcano to them that they think will still erupt, would be the dormant volcano Trindade, which is a ways away from them and in the middle of the ocean.