There is no duty free allowance for alcohol in Singapore so any you take in with you will have to be declared at customs and duty paid on it.
However, I am not sure what the protocol would be if it was in your checked luggage......... but security at Changi Airport is very strict so perhaps best not to p*ss them off.Edited: 13 March 2018, 18:27
Thx for your reply, no I don’t think it would be wise to p**s them off. I suppose if I buy it in Penang airport and then declare it, it may still work out cheaper.
Singapore does not give duty-free allowance for alcohol when you are arriving from Malaysia. You are required to declare any alcohol in your possession (doesn't matter whether it is in your checked luggage or carry-on) and pay the customs duty. The duty rates can be found on Singapore Customs website:
Most wines and spirits incur a duty of S$88 per litre of alcohol. To calculate the duties payable, multiply the rate by volume in litres and percentage of alcoholic strength. For example, a 1 litre bottle of wine with 20% alcohol is charged a duty of S$17.60.