Remember mood rings? Slip one on and the psychedelic stone would carefully ponder your mood or emotional state and, in seconds, change colors to reflect whether you were happy, sad, anxious, calm, romantic, or, sadly, just average. As kids, this “scientific” knowledge was power—now I know I’m miserable or cheerful or nervous. But what could I do with that information?

Although my mood ring has long been packed away, this simple go-anywhere indicator seems to have a thriving, high-tech cousin that’s taking center stage with digital marketers—meet mood technology, rapidly emerging in step with the proliferation of mobile access and integration. Over the last few years, many insiders have argued that mobile technology is all but forcing brands to consider the moods of its users, more so than any other media or platform before it. Apple even went so far as to submit a patent for a mood-targeting technology, which takes into account historical and contextual inferences and data to create base profiles for users. As those users move above, below, or to the right and left of “base,” content and brand messaging can be delivered, based on where that person is in relation to his or her personal norm. In other words, your smartphone knows how you should feel, and serves up a host of offerings based on how far you veer from that emotional position.

So what goes into these mood assessments? Lots, including biophysical reactions and responses such as heart rate, adrenaline level, perspiration, body temperature, and even vocal indicators such as pace, tone, pattern, and perceived stress. If you aren’t great at reading people, this technology will no doubt give you a run for your money in the interpersonal engagement arena. And it also opens up an interesting ethical debate. Should I, as a marketer, be tapping into seemingly personal or private information about you so that I can drive click-throughs or make a sale?

Taking it a step further, these omnipresent mood gauges will look at your interaction with your chosen platform and device—how hard are you hitting the touchscreen, how quickly are you moving between apps or content pieces, are you clicking fast or lingering, and, of course, the who/what/where/when of it all: what time of day is it, where are you, and where have you been? Compound that with things like social media status updates, music selection, and content consumption, and discerning a user’s mood suddenly seems like a no-brainer. When your younger self slammed the bedroom door and put on loud music, your parents didn’t need a mood ring to know you were not happy.

At its most basic form, marketing is about connecting consumers to goods and services. Digital integration, targeting extensions, and personalization paved new in-roads, all but guaranteeing those connections would be made when the consumer needed them most. Mood targeting takes that context to the next level, homing in on moods and the specific moments associated. What’s more, it can dig deeper on otherwise accepted engagement metrics—did I spend all that time reading the blog post or searching for a new pair of sneakers because I was really that engaged, or was it because I was stuck at the airport or in a doctor’s waiting room? The technology knows, because it can discern the enthusiasm from the boredom.

Beyond mobile, this type of targeting is a no-brainer for wearable technology—I explored some of these ethical questions in my series on wearable tech a few weeks ago. It’s rumored that iWatch will have some content-delivery mechanisms that are triggered by, in part, the wearer’s inferred mood. It could potentially go pretty far in that arena, with things like mood-sensing dresses that flap based on the wearer’s emotions, and bras that sense stress. Some of these pieces can even text select contacts when you’re feeling a bit blue.

The applications for mood targeting seem to fall perfectly in line with industries such as medicine and personal care—you know the wearer is having heart palpitations, panic attacks, or particularly high levels of stress and anxiety. But what about other types of targeting? If I’m feeling sad will my smartphone—or tablet or watch—push a coupon for ice cream? Or a great event happening in my area? Maybe a funny video or distracting article I might enjoy? A sale at my favorite store? A new song from an artist I love? Is there a market for tapping into bad moods and giving people that artificial boost—and could relevant, almost clichéd brands benefit? Taking it a step further, can these targeting devices start to learn your patterns and, presumably, detect trouble ahead and try to deliver content, offers, or even reach out to friends and relatives, helping to reroute your bad mood completely? Or, anticipating you might react out of frustration, your smartphone could warn you not to send that email—you hit those keys pretty hard—or make that phone call, if it detects tension in your voice.

If I dug up my old mood ring it would no doubt work just like it always did decades ago. It would turn violet and confirm that, in fact, I’m in a good mood. When my hand gets hot—from stress or, just as likely, from running up the stairs or holding a cup of coffee—it would proudly tout that I was nervous. But with a mood ring, there would be no one standing by to tell me to take a deep breath, text a friend or maybe even go for a run in new Nike sneakers, have a Bud Light, or, heck, even a Xanax. But, tomorrow, my phone will. And what that means for marketers, brands, and, especially, consumers, is a whole new level of connectivity, targeting, optimization, and content delivery that’s both uncomfortably omnipresent and as uniquely aligned and exciting as virtually any new technology has ever been. And it’ll never turn your finger green either.