At the Singapore airport there are baggage storage facilities at each of the 3 terminals, both airside in the transit area and outside in the public areas. So there are 6 places you can leave your hand luggage.

Also, all three terminals are connected on the airside. So you can sleep at the transit hotel at terminal 1, wake up in the morning and go to terminal 2 on the airside, leave your bad within the transit area in terminal 2 or go through immigration and leave your bag in the public area in terminal 2.

I have done both, leave my had luggage airside as well as outside. The only thing is that if you leave your hand luggage airside, you need to carry your passport with you in to the city. If you leave your bag after you go through immigration, then you can leave your passport and other travel documents in your hang luggage at the luggage storage. Things are pretty safe in Singapore, but just make sure to lock your luggage.

By the way, if you search for "luggage storage at Singapore airport" on Google, it should show the relevant info on the SIN airport page:

http://www.changiairport.com/en/airp...e-storage.html