Generally, country boundaries have a fence marking the borders. When illegal border crossing takes place it is done through underground tunnels. while digging these or moving through this fence will vibrate. we will install such a system on a drone that would calculate the frequency of vibrations that should be there (according to weather, wind speed etc) if the frequency exceeds that calculated by our program then obviously some other force is present a possible border crossing is going on then the drone would send an SOS message.
That seems highly inefficient. Consider the fact that you cant exactly visually measure some shakyness. The vibration of the ground or anythint like that. Second, being it being a drone it will be far more shaky and air under it far more disturbed than you’d think. Your device would measure wake turbulence more than anything else. Third, the drone in itself is inefficient because it runs on batteries and cant do more than an hour or so of surveilence (today at least, even with solar charging). Fourth, the so called digging of tunnles will happen, if it ever happens like that, by a shovel, not a buldozer. So you wont be able to pick that up either. Given that I am writing from them phone I might have missed some point. But generally the way you described it wouldn’t work and wouldn’t do the job you want it to do.