Well I was think that the sensors should be on all the time. Switching on and off will be a hassel and may not remember. But I feel the sensor sound should be allowed to turn on and off.
Arethere any such good sensors available the market?
You can buy Front sensors specifically (from Aliexpress) and fix them to sense the speed. Below 10/20 kmph, they will be active. Above that speed, they will switch off automatically. Although there are lot of generic front sensors with ECU hook up, I know of only 'Parking Dynamics' through a colleague of mine, but it seems to be costly.
I have to use fuse also? How to connect wire to the system and switch?
If you want to use switch only system (without the speed sensing ECU hook up), you need not use the fuse. As for installation, I can point you to GP road in Chennai where there are competent accessories fitting shops (Don't know about shops in Delhi). Note: I and my friends' circle have never done a DIY project. We have used only competent accessories fitting guys.