You can receive rewards for gathering a variety of collectibles and performing repetitive tasks around the city of Chicago, either by intentionally scouring the city for points of interest or simply by stumbling across events as you explore.
There are 23 songs you can obtain by hacking phones people are using to listen to music. As you hack pedestrians, there's always a chance you'll find a new song.
You can increase your odds of finding songs by unlocking the Profiler Optimization ability from the Skill Tree. It will highlight hacking frames in vibrant blue, so you know you'll get something special like extra money or a song.
You can spy on the various residents of the city, by hacking into boxes (usually after tracking wire along several boxes), or sometimes by solving hacking mini-games instead. You'll see conversations or strange routines as a reward for your trouble.
The hacking mini-games are solved by turning elbows and T-shaped pieces to allow current to flow to locks which, once eliminated, provide you with more pieces. Once you unlock the last lock in that manner, you'll get through and have a nice view of your target. The actual invasions are easily enough accomplished that I won't ruin the surprise by outlining what you find once you invade at each individual point.
Find all 30 points specifically earmarked by the game's developers (look for the icon of the eye on the world map) and you'll receive rewards at various stages of completion: the Vespid 5.2 vehicle, the Sunrim vehicle and finally an achievement/trophy.
I've provided a separate page with more information about the troublesome towers (see the Table of Contents to the left). In general, the idea is that you hack into the ctOS towers and as a reward, you'll receive notification of points of interest on the world map.
As a bonus, you will also pinpoint the location of hideouts, which you can use to easily warp around the city. If you're trying to do everything in the game, it makes sense to hack the ctOS Towers as a starting point.
There are 16 points where you can complete ctOS Breach contracts. Your reward when you finish is an achievement/trophy.
Breach locations are marked on the map. Once you hack the first point, you'll have to quickly find other points, by using cameras to save yourself travel time (in some cases) and by hopping into a car or convenient boat and driving when the location of a point is further away.
You'll hear an Audio Log recording as you finish each breach. Most of them are easy enough to figure out, but note that there is one location near the train tracks along the north side of Brandon Docks where you must reach a high ledge and climb up some stairs to trigger the breach. The only way to reach that ledge is to pull a dump truck around, then climb onto it and from there onto the platform. I must have spent a couple of hours messing around before I figured that out finally.
There are 100 check-in points around the city. You can find them marked on the map as checkpoints, and you'll want to check into each of them to earn a trophy/achievement.
Other players can check into those same places within the city, so it's a bit of a competition.
You'll find Audio Logs all over the place, as you work through the campaign or just as you explore Chicago. You are rewarded with an XP bonus once you have scanned 10 of them.
Even after you find the initial 10 logs, you'll continue to find more of them all around the city. Audio Logs are available as part of numerous missions and investigations, so don't fret too much about any risk of missing out on the XP bonus.
NEXT: ctOS Towers