I know what you mean. The vets' called them “gnomes”. The locals called them “gnomo”. Sometimes you hear “gnomu”. In most languages it is “gnome” or “gnom”.
They're little robots, about a quarter of a metre or less. Most are like stout crabs or tailless lobsters; woodlice, perhaps. Some are like helmets with legs, like those things at the beach, you know, limpets. Others are like mushrooms, but the top part is armour. There are supposed to be some like stick-insects, but I never saw those. Or perhaps I did and didn't realize.
What do they do? “Area denial”. Back in the day if you wanted to defend something you scattered mines around and strung up some barbed wire. Then some poor sods had to sit in foxholes to make sure no one cleared it all. Now you just dump a couple of crates of gnomes in the area. You don't need the mines and wire.
The gnomes will watch and listen. They don't get bored, or fall asleep. They don't care they are cold and wet. There is no point in shelling them. Their armour stops fragments, and they don't get shell-shock. Most of them are burrowers, and they dig deep. Deep enough to escape all but the really big blasts. If the burrows collapse they just dig their way out. Not like they can suffocate. Thermobarics are not much more effective. They can handle heat and pressure.
Typically a gnome has a pod or two of micro-missiles. They are hard to fight because their size makes them hard to spot. And their thick armour will often shrug off a bullet. They'll hide under bushes or up trees. Even make little trapdoors or hides. They will take turns firing at you from different directions. Disappear down a burrow and pop up somewhere else. Gnomes are not built for long-distance travel, but they can move pretty fast when they need to.
Often they will not fire at you directly. There will often be some mortar-bots somewhere close. There are probably pallets of VLS missiles buried in the area too. If a gnome sees you it will drop rounds right on top of you. They use lasercom and receivers connected to fibre-optic hard-lines. Weirdest thing is they also communicate by sound and call to each other to coordinate. Sounds like whistles or insect-calls, but it is high-speed binary. Some of that is outside of your hearing range. Gives you a creepy feeling! 
And if you think they are a pain out in the countryside, you have never met any in an urban environment. They can climb vertical walls, so get all sorts of places. They will be under rubble, under vehicles, in gutters, anywhere.”