Signal Detection may sound like a dry topic, albeit one Nate Silver wrote an entire bestseller about (The signal and the noise). This chapter starts with a conversation between myself and my friend Abby about her abysmal luck in online dating. Her luck and strategies become the core of the chapter and are used to explain what happens when we miss signals (i.e., Mr. Right) or accidentally keep dating Mr. Wrong for way too long. My friend Seth is a counterpoint: he is too cautious to date the number of women it will take him to find Ms. Right. Fortunately, the site OkCupid was also interested in this kind of signal detection and published their data in blog posts and in Dataclysm: Love, sex, race, and identity - What our online lives tell us about our offline selves. I input their data into a signal detection analysis, showing just how we know whether Abby and Seth will ever find love (with chart). From here, the examples turn more serious: medical misdiagnosis, DNA analysis freeing the wrongly convicted, false alarms resulting in painful biopsies, and of course the unending arms race between terrorists, the TSA, and the family that just wants to get a full tube of toothpaste to Disney World. Even animals participate in signal detection: The US government attached trained pigeons to the underside of helicopters because of their capacity to find capsized sailors floating in the ocean and giant rats are learning minefields in Cambodia and Mozambique. These sections close with a “how to” guide to improving signal detection, both through training and helpful automated systems.