Motorola has unveiled an accessory for its new Moto X smartphone that its marketers claim "provides all the benefits of a PIN without the hassle." That claim is only half right, but you wouldn't know it from a blog post introducing the Motorola Skip and all the headlines that followed. Left out of the coverage are some key protections people may lose when using the thumb-sized clip.

Yes, the wearable fob, when electronically paired with a Moto X, instantly unlocks phones with a simple tap, skipping the step of first entering a personal identification number or swiping a pattern. Making things even easier are three "dots" that accompany the clip and can be affixed to desks, bedside tables, and other trusted zones. Paired phones can be unlocked by tapping them on the tiny stickers—again, with no PIN or pattern required. Assuming it takes 2.3 seconds each time a four-digit PIN is entered and people unlock their phones from 39 to 100 times each day—as Motorola figures claim—a device like Skip can save huge amounts of time over the lifetime of a phone.

But as is almost always the case with security, the added convenience comes with a cost. In exchange for making things easier, people who use Skip may be vulnerable to several threats that are impractical against mobile devices protected only by old-fashioned personal identification numbers.

The most obvious risk involves theft or loss. Skip is small enough to be carried in a pocket or purse or worn on a lapel. That makes it highly susceptible to being stolen or misplaced. If a thief sees someone on a bus use Skip to unlock his Moto X, the thief will simply demand the phone and the fob. And now, rather than appropriating a device that can't be unlocked, the thief has access to a fully functioning one that includes e-mail, contacts, and apps. Yes, someone carrying out a strong-armed robbery can demand the victim surrender her PIN, but that scenario seems unlikely. The ability to steal or otherwise obtain a highly portable accessory that substitutes as a password doesn't seem unlikely at all.

Similarly, many people use PINs to prevent co-workers, roommates, or even partners from accessing a phone while it's temporarily unattended. The dots that accompany the Skip fob may similarly weaken the PIN protection many users now take for granted. People who place a dot on their workplace desk or their living room coffee table will need to think twice about running to the bathroom without first securing their phone, since anyone who is close by will have complete control.

Skip-paired phones may also be more susceptible to snooping by law-enforcement officers. This risk shouldn't be overstated, since police often have the legal authority to get court orders demanding Google or some other service provider unlock a device that has been seized. But in cases where a warrant isn't practical, use of Skip could make all the difference. Confiscating a fob is no harder than confiscating a smartphone. Since most people are likely to carry their Moto X with the fob, its use could give an officer the immediate ability to unlock a device.

Lastly, given how bad most phone owners' security hygiene is, it wouldn't be surprising to see many people take little care in properly stowing their fobs in a safe place. Just as many people think 1234 is a strong PIN, it's easy to imagine many Skip users clipping the token onto their phone case.

The risks that come with Skip aren't necessarily a reason not to use the new accessory. Still, these are potential threats that users should consider carefully before deciding to use one. The point: security has always been a trade-off between convenience and time-consuming obstacles like PINs. Whether it's Motorola Skip, the fingerprint reader rumored to come with the next iPhone, or some other newfangled way to unlock your device, trade-offs will always be involved. Beware of marketers who claim otherwise.