Watch Dogs
49 Achievements
1,250
Clear Signals
Unlock every ctOS Tower
30
How to unlock the Clear Signals achievement in Watch Dogs - Definitive Guide
There are a total of 13 Towers to hack, and they will only unlock once you've destroyed and hacked the ctOS Central Centers within the area. All should be revealed to you as you takedown ctOS Towers and are shown on the map by a red WD Fox logo icon.
Each Tower has a central unit that you must reach and hack. All are locked behind a gate, which you must find and hack the unit to that to unlock. The best way to complete these little mini-games to head to a Towers location and simply search your surrounds via the ground and by hacked cameras. Use your Smartphone to locate wires along buildings to find the panels you need to hack, and the cameras to seek out any that aren't within reach or sight.
You can view how many you have left if you bring up your Smartphone, select the 'Statistics' App and then press to access the 'Progression' menu.
There are 13 ctOS towers in the game shown with the big red icon. Unlocking them will show points of interests such as collectibles and investigations. Keep in mind that not all points of interest will be exposed on the map until after certain points in the story, therefore if you can't find one and haven't beaten the game then you need to keep playing the main story.
To unlock them you'll need to gain entry to the base of the tower and install a "backdoor". Each of these are basically a puzzle. There will always be at least one locked door that you need to find the unlock panel for.
Here's a guide to unlocking all 13: