Technology is letting us make things smaller, and this miniaturization is occurring in all sorts of things we use like computers. But it is also being used in military equipment and weapons. Making things smaller means we can make some great things, but it also means that we have the ability to enable some pretty terrifying and effective weapons.
The first thing we should investigate is at what point is something considered micro or nano in reference to weapons. Micro means 10-6 th and nano just means 10-9 th and, in some cases, may denote one micrometer or nanometer respectively. Micro and nano, however, it seems are often just used to refer to things smaller than the regular sized version with nano being the smaller of the two. If, for example, the normal size of something is quite large, say a building, then a small size version like a doll house may be called micro or nano sized. In the case of weapons, it seems it’s all relative to the size of what the object is being compared to. In some cases, nano is used more correctly to refer to things on the nanometer scale, but this use isn't uniform.
When it comes to weapons, there are a few technologies currently in use and being researched. Included in those are micro aerial vehicles (MAVs), nanobots and nanobombs.
MAVs are simply very small flying machines. Today, micro drones exist in various forms and are most 
Image credit: DVIDSHUB / CC BY 2.0commonly sold as toys. However, these are still large compared to the MAVs being developed for military use. The military has a few designs using wings that are currently being tested, but they aren’t so micro. Rather, they are more like slightly smaller remote control vehicle size. Most of the really small stuff is currently wired due to weight and power requirements being a problem. Tiny fixed-wing aircraft are also in development as are mini helicopter designs that are roughly bird-sized, as well as fly sized vehicles that may even look like insects. To improve stability, designs that use a flapping wing method of flight are being investigated as they have some inherent advantages. Designs with flapping wings are typically called ornithopters and they allow the MAVs to be more stable by compensating for instability in the air with wing adjustments.
Fixed wing designs have traditionally been the most successful and may still be included in some designs as they also have benefits. Power is an issue for MAVs as well as radio transmission of data and control signals. To combat these issues, the devices may need to be semi-autonomous and also be able to use power from various sources in their operating area. Power such as wind, solar or tapping into power from power lines are ways that these devices could be able to operate. The small vehicles can be used for surveillance in otherwise hard-to-get places and be the proverbial fly on the wall. They may also carry small explosives or poison such that they could kill or incapacitate a victim without being detected.
Perhaps you are thinking that such small weapons can’t do much, and perhaps it is difficult for a fly to carry much in the way of explosives or poison. The great or terrifying thing about very small things is that you can have lots of them in a small space. A swarm of MAVs could carry enough of something to do a lot of damage to one or more persons. A swarm can also put cameras and microphones all over, making it impossible to hide.
How real are they? At the moment, MAVs are still in the R&D phase, although some prototypes have been made and tested. Power is still a big issue for the really small stuff as batteries add weight and the rf transmission needed for control or surveillance also presents a problem as it uses power. Fly- and dragonfly-sized versions have been built and tested but are typically tested while tethered to power. If weapons have been added to these tiny versions, they have not been made public. Fixed wing designs in the bird and slightly larger size ranges have been built and tested as well. These are being tested as swarms of vehicles flying pre-defined patterns and being assigned missions. Other designs in the bird sized range are also being tested.
Nanobots are typically talked about as a future tool for doctors. These are tiny machines that can go inside 
our bodies to repair or otherwise modify things inside us. These are currently the smallest of the devices on the list and may have components in the nanometer scale. They are being designed to flow in veins or in other places inside our bodies. As an example of potential nanobot capability, the devices are able to deliver drugs to very specific locations inside the body such that effectiveness is increased and side effects are decreased. More advanced nanobots may be able to do more complex things such as operations from the inside. The very nature of what nanobots do makes them a possible weapon. Delivering small doses of drugs to specific points in the body or otherwise modifying things inside our bodies can be used to kill or otherwise alter an individual from the inside. Currently, nanobots are only in the R&D phase and weapons won’t likely be the first use of them. Just based on their potential, you can be sure that once developed, using them as weapons won’t be far behind.
Micro or nano bombs are basically what they sound like: very small bombs. The size of these bombs vary from truly microscopic to a nuke that could fit in a hand bag. In the case of microscopic bombs, the explosion they create may not be very big or even noticeable. It could, however, be used inside the body to deliver its force at a precise location. Nano in the case of a nuclear bomb may be misleading because the sizes of the bombs are often not microscopic but are very small compared to their full-size counterparts. A nano nuclear bomb, for example, may be on the scale of a soccer ball or baseball while having a yield of around one hundred tons of TNT, which is enough to take down a large building. In comparison, the same size non-nuclear explosive is a tiny fraction of even one ton of TNT in power. To give you an idea of the scale, the Oklahoma City bomb was roughly equivalent to two and a half tons of TNT. I don’t know about you, but that kind of power in that small a package makes me very afraid. At one time, nuclear bombs that would fit in a backpack were being developed. However, whatever was developed has never been publicly shown. The smallest nuclear warhead known to be manufactured was 11 x 16 inches in the bare package and even that size is quite a scary thought.
It is clear that the shrinking of technology is not only possible but happening, and that many new weapons will be possible as a result. Warfare in the future may look very different, but let’s all hope we never experience any of these weapons first hand.
