A prison in the Brazilian state of Santa Catarina recently replaced its guard dogs with a flock of geese that supposedly make loud noises when they detect strange noises, like someone trying to escape.

In this day and age, prison complexes feature state-of-the-art detection systems that make it very difficult for inmates to escape undetected. Still, regardless of technological advancements, it’s always a good idea to have a backup analogue detection system as well, in case the sophisticated stuff fails. Human guardians and guard dogs are usually the norm, but some prisons use some unlikely alternatives. For example, several prisons in Brazil have replaced guard dogs with geese, which they say are not only just as effective, if not more so, but also cheaper to maintain. Apparently, geese have excellent hearing and will make loud noises whenever they detect strange noises, thus alerting the human guards.

“We have electronic surveillance, in-person surveillance … and finally the surveillance of the geese, which replaced the dogs,” prison director Marcos Roberto de Souza told Reuters. “Nighttime is very quiet. Even during the day as you can see it is a very silent place and at night even more so… The space favours this type of security in the case of the geese.”

The flock of “geese guards” patrols a space between the prison’s inner fence and its main outer wall.

Brazilian prisons have been relying on geese to keep inmates from escaping for at least 12 years now. Back in 2011, the Sobral prison in Sao Paolo made international news headlines for introducing a hissing flock of geese as a means of alerting the human guards to suspicious activity.