If someone has ever told you that you "might be hearing things," direct them to the prank pulled off by a trio of 20-somethings who used just a speaker and an iPhone to make shoppers think they were losing their minds.

DJ Sennett, a 21-year-old musician and prankster with his own YouTube prank channel, and two friends, Andrew Scites and Justin Stuart, recorded themselves saying phrases such as, "I'm stuck in here," "Excuse me do you know what time it is?" and "Hey, I like your shirt" into a mic at home.

They then transferred the recordings onto an iPhone and set out with the iPhone and a mini-speaker to a local grocery store and a construction store in Denver, Colo., last week.

In a behind-the-scenes video Sennett and his friends posted on YouTube, the trio showed how they set up the prank in the construction store. First, they found the perfect disguise for the speaker - black bags - and then placed the speaker under the bags in a shopping cart.

They would then leave the cart in an aisle unattended and stand back and watch their prank unfold.

Shoppers' hilarious reactions to the seeming "voice from nowhere" were recorded on one of the prankster's iPhone cameras. The resulting YouTube video has garnered over 200,000 views since it was posted Tuesday.

Sennett is the prankster behind other gags like drinking a blue sports drink from a Windex bottle and squeezing silly string on people, all recorded for posterity on YouTube.

In March, however, the Los Angeles resident turned his pranks into a good deed by handing out food to homeless people in his hometown while dressed as a waiter. The YouTube video of Sennett as a waiter has garnered more than 500,000 views.