AirTag

AirTag launched at $29 for a single unit, or $99 for a pack of four. 

It was a small, glossy white disc with a polished stainless steel back, and Apple offered free engraving at checkout, letters, numbers or a small selection of emoji, so you could personalise one before it arrived. Power came from a replaceable CR2032 coin cell battery rated to last over a year, rather than anything you'd need to plug in to charge.

Alongside standard Bluetooth, it included Apple's U1 Ultra Wideband chip, which on iPhone 11 and later let the Find My app show a precise on-screen arrow and distance to a nearby AirTag rather than just a rough signal strength, something no simple Bluetooth tracker could do at the time. If it was too far away for that, it could be tracked anonymously through the wider Find My network, made up of hundreds of millions of other Apple devices. A small built-in speaker let you play a sound to help find it nearby, and it was rated IP67 for resistance to water and dust.

It was also built with privacy and misuse in mind from the outset: if an AirTag that wasn't yours seemed to be travelling with you, your iPhone would alert you to it. That system came under public scrutiny not long after launch, with reports of AirTags being used to secretly track people, and Apple strengthened the detection and alerts through software updates over the following year in response.