How to to view wifi signal strength ?

there is a command which you can use for it , it is very simply

open terminal and enter :  watch -n1 iwconfig

wlan1 IEEE 802.11bgn ESSID:”WIFIİHOST” Mode:Managed Frequency:2.412 GHz Access Point: xx:xx:xx:xx:xx:xx  Bit Rate=58.5 Mb/s Tx-Power=20 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:on Link Quality=39/70 Signal level=-71 dBm Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0 Tx excessive retries:453 Invalid misc:1679 Missed beacon:0