what is the lowest speed it will pick up

The standard SR3600 is designed to work between 10-255 MPH or the equivalent in KpH. If you need something that will read down to 4mph choose our SR3600-LS. Our SR3800-LS will read from Speed range is 2mph to 250 MPH SR3800-ULS can be purchased to read from Speed range 0.5mph to 31.5 MPH SR3800-PL/FL can be purchased to read from Speed range 3mph to 60 MPH Please contact factory for specials listed above. Standard SR3600 & SR3800 available for purchase from Amazon.

What is the power source; batteries or rechargeable?

Power: 2 standard 9 Volt batteries (alkaline type recommended) Battery Operating Life Over 5 hours of continuous use, typical 50 hours in trigger mode (without the optional remote display's DL431 or DL834 attached). If using with the DL431 batteries will last approx 0.5-2 hours Using the SR3600 with the DL834 will not work on batteries only. Power Supply Options available: 9VDC for use with the Sports Radar gun and/or DL431 display. 12VDC for use with the Sports Radar gun and the DL834. Only one power supply needed to work the radar and display.

Can i connect this to an external lcd screen of my choice, can it display the speed on a laptop screen or a standard lcd screen?

Hello, You can connect to any computer monitor with our SR-PC-02 software. The LCD screen if you are talking LCD monitor it has to be connected to a PC that is running the software. You can also write code to talk to a monitor but you will need a PC, or Raspberry PI that sends the data to the LCD. We provide the data protocol with the software package that allows you to write your own code.

can you calibrate this gun

The SR3600 uses a fixed frequency speed sensor that needs no calibration. Factory recertification is available, please contact us/factory direct for calibration services.