Deus Ex Machina in an exploration into a fan remake and modernisation of the original in Unity, redesigning systems and game mechanics to conform to modern iterations of the franchise and the genre as a whole. Not designed to be an exact remake of the original but instead and evolution of it with the intention being at this early stage to produce a reimagined Liberty Island as a portfolio piece.
Multitools are one component in the realm of hacking in this project and form part of the complex functionality between Augs, Skills and Hacking Software. They are a specialised tool used to provide a means for less skilled players to circumvent security systems automatically where they normally wouldn't have been able too.
Found MD's explication for this puzzling as bombarding any circuit with enough microwave energy would have more chance of just frying and melting it than producing any form of benefit in the way of circumventing security measures.
A more plausible explination would be a tool that wirelessly connects to the device and then runs through a preset load out of hacking tools in an attempt to utilise any exploits it can find to gain entry. Very useful for players who do not have a high focus on hacking but the tool is not very effective against more advanced private and military grade security systems, but is effective against most key pads, electronic locks, cameras and your internet connected toaster.
[Update - 27/10/17]
All hackable devices have a security rating ranged from 1 to 10. If a device has a security rating above 4 then successfully using the multitool on the device will reduce it's security rating to allow for a subsequent successful attempt to allow the player to gain entry. The amount the security rating is reduced is also random between one and four points. higher security ratings will not only be more difficult for an attempt to succeed, but a successful attempt will yield a smaller security point reduction.
If in the event an attempt is failed, the firewall defensively attacks the device rendering it useless, so best keep them updated to ensure you are using the latest versions of exploits and zero days. These devices are also not thrown away after one use, but to compensate for their value, they are much harder to come by.