Why don't you install a burglar alarm in your house

1. why don't you install a burglar alarm in your house 
-> I suggest__________________________
2. what about going out this evening ? 
-> Let's___________________________
3. Let's collect old clothes
-> I think____________________________
4. I suggest that you should drink a lot of water 
-> why we____________________
5. How about going to work by bikes instead of motorbikes to save energy ?
-> Shall we ___________________