KTV Pro+ Ai Alert Rear

The Lezyne KTV Pro+ Ai Alert Rear is a light, compact tail light with one trick that changes how the traffic behind reads you: when you slow down, it knows, and it flashes hard to say so. It weighs 50 g, charges without a cable through a USB stick built into the body, and straps to round, aero and D-shaped seat posts.

Who it's for

Commuters, road riders and bunch riders who share the road with cars and want drivers to see them braking before the gap closes. Think of the run home along a busy arterial in the evening, the stop-start of city traffic, or a Saturday bunch where the rider behind needs warning that you are easing off. It is also a neat second light for a bike that already has a big tail light, because it costs you almost nothing in weight.

Brightness and runtime together

Six modes trade output for hours:

• Day Flash: 150 lumens for 10 hours 30 minutes, for daylight on busy roads
• Blast: 50 lumens solid for 2 hours
• Pulse: 50 lumens for 4 hours
• Flash 1: 25 lumens for 18 hours
• Economy: 10 lumens solid for 9 hours
• Femto: 5 lumens for 20 hours

In any mode, Ai Alert watches for deceleration and switches to Active Alert, a rapid 150 lumen flash, whenever you brake. It comes pre-programmed, needs no app and collects no rider data. If you ever want it off, hold the button for five seconds with the light switched off, and do the same to turn it back on.

Beam shape

Wide Angle Optics spread the light across 270 degrees, so the KTV Pro+ shows from straight behind and well round to each side. That side spill is what a driver pulling out of a side street or across a roundabout actually sees.

Charging and battery

The 400 mAh battery charges through a USB stick built into the light, so it plugs straight into a laptop or USB wall block with no cable to lose. A full charge takes about 3 hours, and the indicator LEDs show the charge level in green and red.

Mounting

The silicone rubber strap fits round and aero seat posts, and a D-shape adapter seats it on D-shaped posts. Line the light up with the bike so it points straight back, and it comes off in seconds when you lock up.

Weather resistance

The KTV Pro+ Ai Alert is tested to IPX7, so a wet commute through a summer storm or a hose-down after a gravel ride is part of normal life for it.