Foxiest of the Hounds is an achievement/trophy in Deus Ex: Mankind Divided. It is awarded for completing the game without setting off any alarms. It is similar to the achievement of the same name in Human Revolution.
Progress towards the achievement can be checked by noting if you have been awarded the "Smooth Operator" bonus after a mission. This bonus is only given if no alarms were set off, so if you missed one of these bonuses, the achievement will not be given.
It should be noted that simply getting all the bonuses does not guarantee the acquisition of the achievement. If, for example, the player leaves a body of a knocked out enemy in a place where other patrolling guards may potentially find him and completes the objective fast enough they will still get the Smooth Operator bonus. Eventually, the body will be found and guards will sound an alarm (it may even happen out of the player's sight), which in turn will nullify Foxiest of the Hounds. So it is recommended to play cautiously and not to trust the XP rewards too much.
- Failing to hack civilian devices or devices in areas that do not contain alarm systems will not void the achievement.
- Make extensive use of hacking software to give yourself an easier time. If all else fails and the countdown is nearly finished, immediately disconnect and try again. If a hack is on its last try, use a Multi-tool.
- Invest in Hacking: Stealth to reduce the risk of detection, Hacking: Fortify to improve owned nodes' security ratings to buy more time, or just grab a few Multi-Tools for use when needed.
- Disable as many alarm panels as possible.
- Stealth is not at all required to get this achievement. One can run about gunning down everybody in the area so long as nobody makes it to an alarm panel.
- NPC states such as guards becoming hostile, search phases and panic do not affect achievement progress, however the same NPCs may seek out an alarm panel, therefore it would be prudent to have a means to quickly neutralize them, or try to avoid triggering those states altogether.
- Cameras, drones, mounted turrets, and bots, however, are often connected to alarms electronically. Therefore, avoid turning cameras, drones, turrets, and bots hostile. This includes turning them to attack your enemies.
- If you did 01011000, Eliza will help you out during Martial Law to get into Dvali territory. The explosion will not void this achievement.
- Certain actions will automatically trigger an alarm, regardless of whether an alarm panel was actually used.
- During M7: The Rucker Extraction, failing the debate with Talos Rucker will cause an alarm.
- During M10: Facing the Enigma, escaping the drones by going into the sewers will cause an alarm. Therefore, escape through the elevator shaft instead of the sewers.
- At the beginning of M13: G.A.R.M., you must contact Alex Vega when the option comes up to contact her or Jim Miller. If you contact Miller, an alarm will automatically go off later in the mission and ruin your chances of getting this achievement. (Alarm triggered after contacting Miller DOES NOT ruin your chances of getting this achievement - confirmed on 22.02.2017).
- During M15: Securing the Convention Centre, during the "Quietly Neutralize All the Guards (secondary)" objective, you must neutralize all the guards with objective markers. Failing to do so will result in an alarm being sounded.
- The achievement's name is a reference to the FOXHOUND black ops unit of the Metal Gear series whose primary rules of engagement involve covert infiltrations and espionage.