“Serial Numbers on Cash Are Not a Control Instrument – They Are a Tool for Security and Truth-Finding” – An Interview with Gerrit Stehle

Have you ever wondered whether cash can do more? Gerrit Stehle has asked himself this question in depth and answers it today with a confident “Yes, absolutely!” Thanks to the individual serial numbers, banknotes can be used for investigations, plausibility checks, and the analysis of cash flows. In this interview, we speak with the CEO of Elephant & Castle IP GmbH about how a digital inventory of serial numbers works in practice, what opportunities the technology offers, and whether existing data protection concerns are actually justified.

Serial Numbers as Unique Identifiers

ALVARA: When did you realize that serial numbers can do more than just mark origin – that they can tell the story of cash?

Gerrit Stehle: Actually, it wasn’t a single moment, but rather a series of contradictions. On one hand, cash is portrayed by some as a security risk – as the “root of all evil.” A lot of mischief is done with it, which could be more easily uncovered thanks to serial numbers. On the other hand, concern arises when the traceability of cash is discussed. This is where data protection concerns come into play – whether justified or not.

The irony is: If serial numbers on banknotes really posed a data protection risk, one would first have to ask why an individual number was printed on each note in the first place. The serial number has always been part of cash. It makes banknotes uniquely distinguishable, regardless of whether this information is technically evaluated or not. And you have to admit: this idea was brilliant. The serial number was one of the smartest inventions to ensure security and trust in cash – an absolutely clever mechanism that still works today.

Serial numbers are also thoroughly proven. For all other valuables in the EU, they are insisted upon and handled with great care. Phones, cameras, machines – it’s standard everywhere. Only with cash does this logic suddenly stop.

When I saw how often cash plays a role in investigations – and how little technical support exists – it became clear: this is not a theoretical problem, but a structural deficit.

You say that recording serial numbers is the most normal thing in the world. Why is it such an emotional debate specifically for cash?

Gerrit Stehle: Because cash is immediately linked to the “transparent citizen” – even though that is technically not true. We don’t record people, purchases, or profiles. Only serial numbers, location, and time.

In all other industries, serial numbers are a prerequisite for quality assurance, product protection, or traceability. With cash, suddenly a small number of people frame it as a fundamental ideological debate. It’s less technical and more ideological.

Where do you see the biggest misconception in this debate?

Gerrit Stehle: That people think cash must either be completely anonymous or fully controlled. That is a completely wrong approach.

Even today, there are countless data points in the cash cycle – they are just not used systematically. We are not talking about continuous surveillance, but targeted nodes, for example in cash centers. Coverage of ten to fifteen percent is often enough to verify or refute investigations.

And one must not forget: the serial number was a brilliant invention. It made cash secure in the first place – it creates trust, enables authenticity, protects against counterfeiting, and remains one of the smartest mechanisms in our monetary system. It’s paradoxical that precisely a security feature that has worked for decades is suddenly seen as a risk rather than a strength.

Truth-Finding Instead of General Suspicion

Elephant & Castle has acted as an expert in over 300 criminal cases. What do serial numbers actually achieve there?

Gerrit Stehle: They help in truth-finding – in both directions. Sometimes they confirm the prosecution’s statements, sometimes they completely exonerate defendants. It’s not about convicting someone, but about making statements verifiable.

In one specific case, it was claimed that cash came from wealth accumulated over years – but the serial numbers showed that the notes had only been printed a few years earlier. That can be decisive. Our technology is therefore not meant to “catch” anyone. On the contrary: it serves as an instrument for truth-finding – factual and efficient.

Despite the obvious added value in uncovering crimes, critical voices are raised. The main concern is that this approach may be problematic in terms of data protection. Is that correct?

Gerrit Stehle: Our digital inventory does not capture personal data. No names, no accounts, no movement profiles. From a data protection perspective, everything is clean.

If you read articles about serial numbers and their traceability carefully, it quickly becomes apparent: the criticism often remains at the level of fears – not concrete legal violations. And honestly, the argument “everything is bad” does not replace a factual discussion – regardless of the topic.

It is important for me to emphasize that there are real data protection experts and so-called data protection experts. Real data protection specialists are indispensable partners for us. They ask the right, sometimes uncomfortable questions – and they concretely show how protection levels and purpose limitations can be further improved. That’s why we involve data protection experts from the very first moment, in every country where we operate. We actively seek their support, jointly specify requirements, and iteratively harden technical and organizational measures. This is extremely important to us – not as a formal duty, but as a mark of quality.

So-called data protection experts, on the other hand, often explain very generally how something shouldn’t be done, without citing specific legal grounds or offering solutions. That doesn’t help anyone – neither citizens’ rights nor investigative quality. Only the “real” experts, in the sense of constructive data protection specialists, provide the crucial bridge between precise requirements and practical implementation.

In the end, we are talking about a clearly structured, four-tiered rule-of-law review process – each level controls the other. Our work is carried out exclusively within the legal framework:

• Security authorities review in advance whether and to what extent the tool may even be used.
• Public prosecutors ensure that only legally permissible information is adopted – to avoid evidence exclusion.
• Judges supervise the proper, lawful conduct of the trial and independently assess evidence.
• Defense attorneys ensure the process is correctly conducted, measures are proportionate, and defendants’ rights are protected.

In short: data protection and the rule of law are not a “counterweight” to our work, but its foundation. We welcome critical, fact-based oversight – because it makes the solution better, safer, and more trustworthy.
 

Unlocking Potential – Thanks to Digital Inventory

Besides supporting law enforcement, where else does the technology bring advantages?

Gerrit Stehle: Ultimately, it all contributes to the digitalization of cash logistics. This means modernization, efficiency, increased security, and, ultimately, cost savings. But not by replacing people – as is often speculated. On the contrary. In times of skilled labor shortages, it’s about relieving employees and using scarce resources more effectively.

A central lever is therefore the digital inventory. If it is always clear where cash is located, a significant portion of duplicate logistics, manual checks, and security processes is eliminated. Today, for example, cash is counted in three stages: at the retailer, in the cash center, and again at the central bank branch. The logistics involved are expensive, time-consuming, and risky.

Systematic recording of serial numbers could be a real game-changer. It creates transparency throughout the cash cycle – and opens up new cooperation models. For example, employees of the central bank could temporarily support private cash centers, similar to the role of BaFin working close to institutions. This could help buffer bottlenecks without reducing jobs. In fact, the opposite is true: tasks would be professionally upgraded and cash stabilized in the long term.

When you know exactly what is in the cash center, logistics costs could potentially be significantly reduced – even in the short term. At the same time, resource management improves considerably. That serial numbers provide the basis for this is already standard in many European countries. For cash, this mechanism exists as well – it just hasn’t been systematically developed to its full potential.

What is required technically?

Gerrit Stehle: Technically, it’s not rocket science. With new machines, we are talking about components in the low double-digit euro range, which then capture serial numbers at the points where counting or dispensing already occurs. So it’s not about new machines or major overhauls, but minimal additions to existing processes.

Software for digital cash management in cash centers also serves as a valuable data source. Cash is already counted, recorded, and forwarded. If all this information is stored digitally, we can save it in our database.

Crucially, not every note needs to be tracked continuously. Even partial coverage at key nodes – e.g., in cash centers or at the first loading of ATMs – provides enough data to digitize inventories, optimize logistics, and support investigations if needed. The efficiency lies precisely in this: high benefit with very manageable technical effort.

Measured against the low effort, the added value is even more impressive. Better inventories, less employee theft in cash transport, lower logistics costs, more security for cash transport, and new investigative approaches for money laundering, ATM explosions, or fraud are already possible today.

What is your central message to politics and authorities?

Gerrit Stehle: Cash doesn’t need saving – but it needs fair and realistic handling. What we are currently seeing are gradual attacks on its role: cash limits, identification requirements for ever smaller amounts, or social pressure to associate every transaction with a digital profile. This creates the impression that cash is suspicious – simply because it exists.

My central message is therefore: cash is not a risk, it is a protective instrument.
It is not the problem. It is part of the solution.
The technology we are talking about – serial number recognition – doesn’t make cash weaker, it makes it safer, more efficient, and fairer.
It prevents misuse without infringing on privacy.
It prevents crime without surveilling citizens.
It creates transparency in the system, not in people’s lives.

And what is often forgotten: cash plays an indispensable role in a country’s cyber resilience.
If digital payment systems fail – due to cyberattacks, hacker attacks on payment services, power outages, or infrastructure disruptions – cash still works. No registration, no app, no server.

This was also evident during disasters like in the Ahr Valley: when power and mobile networks were down for days, cash was the only functioning infrastructure for everyday needs – groceries, fuel, supplies. No digital system could have replaced it.

Finally, this issue must also be considered in the context of geopolitical tensions: in wars or hybrid conflicts, digital systems are often the first target. Cash is then the last stable anchor of civil society. It works offline, independently, resiliently.

That is why it is so important not to weaken cash, but to make it fit for the 21st century. Good technologies – like serial number recognition – stabilize cash rather than threaten it. They modernize it without affecting its core.

The real question for politics and authorities is therefore: do we want to protect cash – or continue to pressure it? Cash is not outdated. With the right technology, it is a modern, resilient pillar of a free democracy.

Any final words?

Gerrit Stehle: Eight years ago, we set out to make serial numbers socially acceptable for cash as well. As mentioned at the beginning: whether it’s a vegetable chopper, a radio, or a PlayStation, all other devices also have individual numbers that make them traceable – sometimes even legally required.

We are open to discussions with politics and central institutions, but are not always heard. We greatly value constructive skepticism. What is missing is the perceived responsibility to check the facts and make clear decisions. But practice already shows that digital inventory can bring more security and truth for our society. And the other possibilities, especially in logistics and cash center management, can provide real added value – if decision-makers are more open. But we persist because we believe in the cause.

And if you have cash at home or in a safe, I can only recommend: write down the serial numbers!

Thank you very much, Mr. Stehle, for the insightful conversation.

Gerrit Stehle: My pleasure. I hope I could champion the digital inventory, which is much more than a business model – it’s a matter close to our hearts.

You did! Thank you.

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