Maybe you were asleep or about to go to bed.

Then, your smartphone emitted a piercing shriek and vibrated rapidly. Tornado warning, the alert said, head to the safety of your basement immediately. This is a dangerous situation.

What? A tornado at night? Don’t tornadoes always occur during the heat of the day?

No, says the National Weather Service.

Two tornadoes touched down in the Attleboro area late Wednesday, waking many from their slumber but sparing most from any serious damage other than downed trees and power failures.

One with wind speeds up to 100 mph started in Lincoln, R.I., before moving to Cumberland and ending in North Attleboro.

The second, in Rehoboth, was only on the ground for a minute, enough time to snap and uproot several trees.

Fortunately, there were no injuries. Still, it made for a scary night.

In fact, perhaps the only thing more frightening than a tornado is one that strikes while you’re asleep.

Tornadoes at night are more than twice as likely to be deadly as those during the day, according to a study from Northern Illinois University.

After examining roughly 48,000 tornadoes in the United States from 1950 to 2005, the study found that roughly one in every 20 overnight tornadoes were killers, compared to roughly one in every 50 daytime tornadoes.

Nocturnal tornadoes only make up about 27% of all tornadoes but are responsible for 39% of tornado deaths, the study said.

Some reasons for this are obvious.

Most people are at home and sleeping at night and can be unaware of an approaching tornado threat. One challenge meteorologists face is getting the public to take shelter immediately, without first “confirming the threat” of a tornado by looking outside.

That’s why it’s so important to have that smartphone nearby when you go to bed.

Here are the two alerts issued by the National Weather Service:

Tornado Watch: This is issued when conditions are favorable for tornado development. People located in and around the watch area should keep an eye to the sky and listen to local broadcast media for further weather information. The watch is intended to give you time to prepare.

Tornado Warning: This is issued when a developing tornado has been detected by Doppler radar or a reliable sighting of a twister. A tornado warning is usually issued for portions of one or two counties, for an hour or less. The storm could also produce large hail and destructive straight-line winds. If the tornado warning includes your neighborhood or workplace, you should seek safe shelter immediately.

The National Weather Service says in general, get as low as you can. A basement below ground level or the lowest floor of a building offers the greatest safety. Put as many walls between yourself and the outside as possible. Avoid windows at all costs.

Yes, Wednesday was a scary night, but we are relieved there were no injuries and damage was minimal.

And we hope it provided a lesson that we must be on guard 24 hours a day.