How to check if a bike is stolen before you pay: serial number, papers and price

You've found the bike you were looking for, at a good price and close to home. Before you pay, spend ten minutes checking whether the bike is stolen. It's easy, you don't need to be a mechanic and it saves you a lot of grief: if the bike turns out to be stolen, you can lose it, and the person who really lost it goes without.

This guide tells you where to find the serial number, what to ask the seller for, which warning signs should make you stop and how to look up the number in the stolen bike alerts on bicis.net.

Where to find a bike's serial number

Almost every branded bike has a serial number engraved on the frame or on a sticker. It's the bike's ID card: it's unique and it's the first thing anyone checks to find out where a bike comes from.

Where it usually is

• Under the bottom bracket, where the tubes meet at pedal height. This is the most common spot: turn the bike upside down or crouch down with your phone's torch.
• On the chainstay or the dropout, near the rear wheel axle.
• On the seat tube, sometimes hidden: you have to take the seatpost out to see it.
• On the head tube, at the front or underneath.
• On e-bikes, as well as the frame, the motor and the battery usually have their own number.

If the number is missing or has been removed

A number that has been filed off, painted over or covered with a sticker is the clearest sign that something isn't right. If the number doesn't appear anywhere, ask why. Some cheap or very old bikes don't have one, but on a mid-range or high-end bike it's unusual.

What to ask the seller for

Someone selling their own bike has no problem showing you where it comes from. Before you meet, ask for:

• A photo of the serial number, clearly legible. That way you can look it up calmly before you go.
• The invoice or purchase receipt, even if it's old. Check that the model and, if it appears, the number match the bike.
• For an e-bike, the charger and the battery keys. An e-bike sold without a charger or key is a red flag: whoever has it may not be its owner.
• Service or workshop records, if it has been maintained. A service history builds trust.

Meet in daylight somewhere busy, test-ride the bike and check the number with your own eyes. If it matches the photo, you're on the right track.

Warning signs: when to stop

No single sign proves that a bike is stolen, but several together should make you think twice:

• A price that's too good. If an almost new bike is selling for half of what similar ones go for, ask why.
• Rush. "I need to get rid of it today", "cash only", "I can't wait".
• They know nothing about the bike: not the size, not the year, not the groupset.
• They want to meet somewhere odd or won't let you see the bike up close.
• There are no papers or photo of the number and they get annoyed if you ask.
• An e-bike without a charger or keys, or with the battery that's "at a friend's house".

What price is "too good"

To tell whether a price is suspicious, compare it with what's being asked for similar bikes. This table shows the median asking price in active "For sale" listings on bicis.net, with the cheapest quarter and the most expensive quarter in each category (data as of 10 November 2026, n = 238 listings, source: Ciclismo en cifras). It's what sellers ask, not the final price.

A price below the cheapest quarter isn't bad in itself: it may be an old or entry-level bike. But if it's a recent, high-end bike, ask for more explanation. To fine-tune, there's the guide How much is a second-hand bike worth?, and if you're after an e-bike, what to check when buying a second-hand e-bike.

Looking up a stolen bike by serial number

With the number in hand, look it up before you pay:

1. In the stolen bike alerts on bicis.net. Go to stolen bikes and search by serial number, brand, model or city. If the bike shows up as stolen, don't buy it.
2. In other stolen bike registers. There are private registers and some town councils have their own. The more you check, the better.
3. In a search engine. Put the number in quotation marks: sometimes it appears in theft alerts posted by the owner.

Not finding it anywhere doesn't guarantee anything, because not everyone reports their theft publicly. That's why the papers and the warning signs still count.

If you find out it's stolen

Don't pay and don't put yourself at risk. If the bike appears in a theft alert, tell the Policía or the Guardia Civil, with the listing and the serial number: they are the ones who can act.

A stolen bike register works for you too

If you have a bike, write down its serial number today, take photos of it and keep the invoice. If it ever gets stolen, report it with those details and post the alert in stolen bikes: that way anyone about to buy a used bike can find it. And if you're looking for a bike, all listings has the second-hand bikes on sale right now.

Frequently asked questions

How can I check whether a bike is stolen?

Find the serial number under the bottom bracket, ask the seller for the invoice and a photo of the number, and look that number up in the stolen bike alerts on bicis.net and in other registers before you pay.

Can you look up a stolen bike by serial number?

Yes. The serial number is unique to each frame. On the stolen bikes page on bicis.net you can search by number, brand, model or city.

Is there a stolen bike register?

There are several: the stolen bike alerts on bicis.net, private registers and those of some town councils. None of them covers everything, so it's worth checking more than one.

What price for a used bike is suspicious?

As of 10 November 2026, the median asking price on bicis.net is €850 for a mountain bike and €2,000 for an e-bike. A recent bike priced well below that deserves questions.

What do I do if the bike I'm about to buy is stolen?

Don't pay for it and tell the Policía or the Guardia Civil, with the listing and the serial number.