There simply is none. Because you have trace amounts of Methanol in every hard liquor as it is created when Pektin is separated during the production. While it can be minimised by proper precautions (right enzymes,right base, etc.) and some liquors carry smaller (Potato,grain based) or higher (fruit based) contents, even professionally produced liquor carries a (very very) small amount.

This does rule out all the “test stripe/kit” sets that are e.g. used in waste water treatment (methanol there is really bad as it means your plant is contaminated and your bacterial cultures are possibly dead) as they only perform quantitative tests - they tell you “yes/no”. But when every test is potentially a yes,it won’t help. (And additionally they are prone to interference by ethanol and some other stuff and need very specific test conditions)

So the test needs to be quantitative - it needs to tell you how much Methanol is there. The only mobile process I am aware of is photorefractometer based - and these need very specific sample preparation that is unfeasible with a drink in a bar. Besides, the cheapest commercial product I am aware of is around 4k and “mobile” is,well, a big word for it - the device is the size of around 4 Nintendo switch consoles. (And each test including preparation takes around 5-10min and costs 20 bucks)

There has been a research project by the Swiss ETH Zurich that claimed that a smaller device has been build,but as far as I know it has not yet reached market maturity so far.

Lastly it’s also a bit of a problem of practicability - do you want to test each drink? Because what happens if the barkeeper changes the bottle while you drink there? Can you still perform the test after one drink? Or two? Unlikely. Can you make sure the testing conditions in terms of temperature,etc. are met?

So in the end you are absolutely out of luck,sadly. But there are a few things one can do besides drinking only in reputable bars or drink no alcohol:

• Stay.the.fuck.hydrated. I know, we all say that a lot, but especially in a warm environment you often aren’t. And in case your body actually encounters Methanol it will need a fucking lot of water to get rid of it as fast as possible (via your kidneys). It’s basically your best bet. Because most methanol poisoning cases are actually never recognised as such, as people simply think they have a hangover,stomach bug,etc. You don’t get blind, you don’t die, you just kill a bit of your liver, heart and brain.

• Immediately stop drinking if you get a drink that tastes like it contains a lot of alcohol but does not make you tipsy - the inebriation of Methanol is far less than ethanol and while you every likely have already ingested a dose that will severely hurt you, it can make a difference. If you start to feel sickish after that get to a reputable hospital asap. There are good hospitals in Vietnam,but they might not be around the corner. (And for fucks sake get travel insurance)

• Watch your surroundings. If the bar you are in is only frequented by tourists despite your location making it normally a likely spot for locals as well this is not a good sign. If the bartender used different bottles of the same brand for different guests it is not a good sign as well. If they use two bottles of the same brand for the same drink? Stay the fuck away. (That’s a common way to hide counterfeit alcohol - you have one legit bottle you use for controls, sometimes for shots especially at the beginning of a night and fill drinks and later rounds up with the counterfeit bottle)

• Now for something a bit more risky: Get a bit drunk beforehand from safe alcohol. No,I am not joking. Methanol competes with regular ethanol for certain enzymes/receptors. By blocking them off before Methanol arrived one can buy the body a bit of time to get rid of more Methanol. (Especially as Ethanol is more competitive). That is why back when I started my career it was not uncommon for a patient to receive ethanol in hospital - or, if that one was “out of stock” for some reason aka an alcoholic pharmacist - to drive lights and sirens to the next 24/7 fuel station as they are allowed to sell alcohol here. Again,that will not safe you,but it might buy your kidneys time.

• If you feel unusually sickish the next morning,like having an extra hard hangover or similar symptoms for the next 48-72h: Get yourself to a doctor if you have the slightest doubt in your alcohol sources. It’s very rare for people to be intoxicated so badly that they are incapacitated directly. Almost all cases die after a latency period of 48-72h before the real bad symptoms set in. If you are able to receive modern intensive care medicine within that time there is a chance to survive cases nowadays that would have died 15 years ago.

Or,even easier: Don’t drink.

(And for fucks sake people: Get travel insurance, don’t drink and drive scooters, and maybe find out where the next private hospital is in the area you travel to. )