I think some posters here are beating around the bush without answering the question -> I will give you a direct and honest answer because I know 2 families who defaulted.
Once you default,
1) CMPB people will ask your parents who live in Singapore to drink coffee with them and ask WTF is going on. If they feel they have been instrumental in assisting you to default NS they will prosecute them in court. However, usually it won't be that easy to prove they have been harboring you overseas (if the house you live in is not under their name and no money trail from their bank account to support you financially) so they will use a series of harassment tactics instead.
2) Harassment tactics include house visits, telling everyone in your extended family that you have defaulted (my friend's grandfather got the brunt of the harassment after his dad finally left Singapore)
3) Withholding certain government monetary benefits
4) take aim at CPF
5) take aim at HDB flat (doesn't affect my friends because they live in condo
No, they won't go to jail and can carry out their business as usual but PAP will try to make their life miserable as though they owed PAP something. Some parents just continue making their $ in Singapore until they deem it enough to retire overseas with their defaulter sons. So far my friends never regretted much as both of them saved 2 years of their prime and managed to access a much higher paying larger labor market in North America where the starting pay is 2.5X of what they will get in Singapore. (unemployment is a problem for the blue-collar class but less so for the educated ones working in hot fields such as IT)
Do not buy into the emergency landing in Singapore and get caught later risk. The chances of that are extremely low -> why? Singapore is not Hong Kong, not Tokyo, and not even Shanghai. There is already a surplus of great transit hubs so what are the chances of a flight being diverted for emergency landing in Singapore when it was headed to Shanghai, Hong Kong and Tokyo? ZERO
So that is their situation. Singapore needs them more than they need Singapore .... for now. However, they have 2 passports: one from the most powerful country in the world and the other from the most resourceful country in the world. Ireland (who needs to be bailed out by EU) doesn't sound to me like it has the ability to print money out of thin air to create jobs or sell black sands for real money so I will really consider serving PAP just to diversify my job prospects. I've served and never regretted because I wasn't clear on what to do with my life at that point and NS was a great vacation I remember very fondly. I am still keeping my passport so I can retire there in the future.
By the way, I hope you are thinking of defaulting because you a career vision to fulfill and not because you hate to pound mud. I always thought National Service = real army life I've seen on American TV but how wrong I was! I can remember my first reaction
when I realized that you can actually go home on weekends and my parents felt more
when I get to go home after BMT even on weekdays (depends on vocation)! Moreover you put military experience on your resume and ang mo employers overseas think you are some solid guy who is disciplined, hardworking and commands respect ROFL.
At the end of the day, you make your own decision and you accept the consequences. I hope that helps.