Apple’s latest media carnival made clear that the company still has a capacity for spectacle, self-congratulation and, in the end, no small bit of innovation.

Amid a multimedia onslaught, including an Elvis Costello performance, the company unveiled the new iPhone 5S, complete with its piece de resistance: Touch ID, a fingerprint sensor that can supplant your password and be used to make purchases from Apple’s various stores.

Even if it flops, Touch ID can still serve a useful purpose. Biometric devices are only going to become more pervasive, forcing consumers to confront a host of legal, moral and practical challenges. Better to start thinking through these issues now, while the technology is still in the gee-whiz phase, than when your bank, employer or (not least) government starts asking for a print.

As traditional passwords have grown more vulnerable, a host of biometric devices — from fingerprint readers to iris scanners — have arisen. The hope is that they could enhance both security and convenience: better protection from hacking and theft, no more forgotten passwords or onerous sign-in procedures. Investors have taken notice, other smartphone makers are likely to follow Apple’s lead, and some of the biggest names in Silicon Valley have joined a trade group that advocates wider adoption of the technology.

In the digital world, however, security and convenience are rarely complementary. Fingerprint scanners have obvious weaknesses that Touch ID will have to overcome if Apple hopes to pave the way for a new era of smartphone security.

For starters, biometric devices are typically susceptible to degradation, fluctuations in temperature or humidity, and the vagaries of biology (the quality of your fingerprint tends to decline significantly as you age, for example). They rely on probabilities; as such they are “inherently fallible,” as a report by the Natural Research Council found. They’re not immune to counterfeiting. And they can be finicky or poorly calibrated — either so permissive they grant access to people who shouldn’t have it or so strict they block your access to your own phone.

If fingerprint scanners are eventually adapted for mobile payments, banking or cloud computing — uses that would often require a database of biometric information to verify a user — they could become as vulnerable to hacking as ordinary passwords. Worse, once a thief has your fingerprint, he always has it.

Finally, biometric data could present a privacy nightmare. It is by definition “personally identifiable,” and if there’s any lesson consumers should have internalized from the past few years, it’s that no data is truly safe once it’s collected and stored.

Apple has tried to mitigate a lot of these problems. The Touch ID sensor, the company says, is made of sapphire crystal, which not only sounds good in a marketing brochure but should also help forestall degradation. Perhaps more important, Apple says that your fingerprint data will be encrypted and stored only on your phone, not in the cloud, thus making violations of privacy or malicious intrusions more difficult.

Consumers may still hesitate, whether because they’re freaked out by divulging something so personal or they find it too cumbersome to bother with. Apple’s challenge, then, is twofold: convincing wary customers that their information is safe and that a fingerprint scan is more convenient than a password.

So applaud Apple’s technological innovation and marvel at its marketing prowess. (Or decry them both; we take no position in the fanboy wars.) Just remember that it’s only the beginning, and that no security system — no matter how cool, convenient or technically advanced — is infallible.

Bloomberg News (Sept. 11)