The devices were set up to record bird songs, but to the group's surprise bat noises were also heard.
"We got the recorders to do bird work and did a sample run for bats and they turned up."
The endangered creatures were detected near Masterton, on Mount Holdsworth, and in the Rewa Bush Conservation Area.
"We found high levels of activity in the areas the bats were found. This suggests there could be reasonable numbers of bats," O'Malley said.
"We hope there are more locations."
New Zealand has two native bat species, the long-tailed bat and the short-tailed bat.
All the bats recorded were the long-tailed variety.
"Since 2017 in Wairarapa, no short-tailed bats had been detected in the Tararua ranges," he said.
"Wairarapa has never been surveyed as a region for the presence of long-tailed bats."
O'Malley said the group hoped to use the devices in other parts of the region to try and find more of the species and find out how many there were.
"We are working with the Department of Conservation to find if there are any short-tailed bats in the Tararua Range and develop a search strategy to find more bats in Wairarapa.
"This summer, we will be looking for bat activity in select areas throughout the region. In Wairarapa, we have a poor understanding of where bats are and how they are doing," he said.
Introduced animals such as possums, feral cats, rats, and stoats were known to eat native bats.
"Both species of native bat are listed as threatened."
Long-tailed bats travel up to 20 kilometres a night looking for food. They move around on a regular basis and were quite small, often no bigger than a finger size in length, with a reasonable wingspan.
They generally eat insects such as moths, beetles or worms, depending on the type of bat.
O'Malley said the group would be heading back into the field later this year and needed help from Wairarapa residents.
They would be returning to places they had been and will search new areas.
"We need help locating other potential colonies. The bats will start to emerge in October," he said, saying they were not active in colder months.
Bats were often found on private land as well as pine forests, conservation areas and even in urban areas.
"Hamilton City has them," he said.
"We would like farmers to contact us to help locate bats on their land."
He said people could also help process data sets and look for roosts.
"As we map Wairarapa, we will start working on a conservation strategy. We are still learning about bats."
