PurposeThis study aims to evaluate the effects of the synergy between monitoring technologies and deforestation control policies promoted by the Action Plan for the Prevention and Control of Deforestation in the Legal Amazon (PPCDAm) during its initial stage.Design/methodology/approachThe triple difference method is employed to explore the differences between the non-metropolitan municipalities with Indigenous lands and other regional municipalities.FindingsThe findings indicate a reduction of approximately 16.1 km² per municipality between 2004 and 2007. This reduction corresponds to a decrease of 10,293 km² in the area of deforestation and a total of 498 million tons of CO2. To ensure the robustness of the results, placebo tests, event study and flexibility in the composition of the groups were conducted. The robustness tests substantiate the findings.Practical implicationsThese results emphasize the significance of remote monitoring policies for controlling deforestation in isolated regions and Indigenous lands. Additionally, such results indicate that the policy was cost-effective.Originality/valueThis study innovates by examining the causal impact of the initial phase of the PPCDAm before 2008, a period not focused on existing literature. Further, employing the triple difference method innovates methodologically to assess PPCDAm's effect on deforestation in isolated Amazon areas.