What information can you extract from Wifi networks without connecting?
The following information can be found when  the device is near a Wifi Access Point (AP) even though the device isn't connected:

Apart from ESSID and Signal strength, 


MAC (for associated access points)
Bit rate
Channel: the frequency channel
Encryption
RTS ("Request to Send") threshold (generally the lower the threshold, the more stable the Wi-Fi network)
Fragmentation threshold 


To manipulate the basic wireless parameters you can use the iwconfig command.


  iwconfig command  is dedicated to the Linux wireless interfaces. It
  is used to manipulate the basic wireless parameters such as ssid,
  mode, channel, bit rates, encryption key, power and much more. To
  display information about wlan0 wireless interface, enter:


iwconfig Interface-Name-Here, 


iwconfig wlan0

To determine an interface, run netcfg

Here is the sample code

$ iwconfig wlan0


and gives the output as:

wlan0     Qcom:802.11n  ESSID:off/any
          Mode:Managed  Channel:0  Access Point: Not-Associated
          Bit Rate:0 kb/s   Tx-Power=0 dBm
          RTS thr=2347 B   Fragment thr=8000 B
          Encryption key: Off