Here's how it works under the basic rules. While it says "most", this is more to say "it's not physically impossible to get a vehicle or drone without one."
They come with a sensor array of a rating equal to the Sensor rating of the drone (for this argument, drones also include vehicles) as listed on pages 463, 465, and 466. While 4th edition had listed in an expansion what "comes standard" in a vehicle, as is, it is not listed anywhere. I would allow a player to pick what functions come in it, especially for drones.
In 4th edition, it was 2 Cameras (front and back), 2 Laser Range Finders (front + back), Atmosphere Sensor, 2 Motion Sensors (pointless in 5th), and a "Radar" which isn't its own function in SR5. I'd probably remove a motion sensor and replace that and the 'radar' with... I dunno, Olfactory and Ultrasound.
I don't believe they can be freely reconfigured; while each function doesn't change the price, it doesn't say anything to suggest you could do that in the book.
You can, however, buy a new one to replace the factory-standard one. The chart on 446 tells you the maximum Sensor Rating for the given drone. A car could go to 7, yes, though remember that during character creation, you cannot have anything higher than Rating 6. Things smaller than a car get different maximum ratings. Motorcycle is 6, Large Drone is 5, Medium 4, etc.
And to be specific, yes, ALL drones have a sensor array. An array. Handheld-devices can hold 3 single-sensors because they have a
capacity of 3, unrelated to their maximum sensor rating. Small or smaller drones have a full sensory
array despite their size, but that is because it is a vital part of their construction.
A Sensor Array is eight sensor functions, taking up 6 total capacity (when added to things it that do not already include one) and allowing the user to replace Perception with Electronic Warfare in certain situations. A Handheld Sensor Housing only has 3 Capacity, and so can only include three separate Single Sensors, each with one function and taking up 1 capacity.
Another interesting question, to me - what's the largest wearable sensor array? Seems to me that 2075 fashion could readily incorporate more than just the handheld sensor.
I could see an argument for a R5 being able to be put in armor as an armor modification. If it fits in a limb, you figure it could fit spread out inside an armor vest or something. Though something nice to know would be how big exactly "wall-mounted" is supposed to be. I have a few picture frames that are huge in my house, but also a few that, if I could roll them up like a poster, would totally be reasonable to fit sewn into the back of a coat or something. I dunno.
