A lost key in a rented flat can become expensive if the key belongs to a lock system. Whether you have to pay depends on whether there is a risk of misuse and whether the landlord actually replaces the system.
In short: If you lose a flat key, the landlord can claim damages. For replacing a whole lock system, the replacement must be necessary for security reasons because of a risk of misuse, and damage arises only once the system is actually replaced. The Federal Court of Justice (BGH) ruled so on 5 March 2014 (VIII ZR 205/13). Last updated: November 2026.
Key points
- Keys belong to the landlord and, according to Stiftung Warentest, tenants have a duty of care. A loss can therefore trigger claims for damages.
- For a lost key to a lock system, the tenant may also owe the cost of replacing the system if that is necessary because of a risk of misuse (BGH, 5 March 2014, VIII ZR 205/13).
- According to the BGH, a financial loss arises only with the actual replacement of the lock system, not with the announcement.
- Whether personal liability insurance covers lost keys depends on the contract. Check before a loss happens.
- Report the loss to the landlord in writing immediately and clarify whether a replacement is needed at all.
Who pays if you lose a key?
In principle you do, as far as the loss is attributable to you. Stiftung Warentest describes that keys belong to the landlord and tenants have a duty of care for house and flat keys. If a key is lost, it can become expensive. According to Stiftung Warentest, how expensive depends on the type of key and on whether the private liability insurance covers the loss of private keys. The legal basis for claims is the general damages law of the Civil Code (BGB), and in the judgment the BGH relies on section 249(2) BGB: whoever breaches a contractual duty and is responsible for the loss must compensate the resulting damage.
With simple cylinder locks and no lock system, the damage is usually manageable: a replacement key or a new single cylinder. It gets expensive when the key belongs to a central lock system that secures several flats and shared doors.
What did the BGH decide on lost keys?
In the judgment of 5 March 2014 (file number VIII ZR 205/13), a tenant returned only one of two flat keys when moving out at the end of the tenancy on 31 May 2010. The owners’ association of the building claimed an advance of 1,468 euros for replacing the lock system. The tenant did not pay, and the system had not been replaced by the time of the decision. The BGH clarified two points.
- A tenant who loses a key belonging to a lock system may also owe the cost of replacing the system. The condition is that the replacement is necessary for security reasons because of an existing risk of misuse.
- A financial loss arises only with the actual replacement of the lock system. A mere intention or announcement is not enough.
The BGH relied on section 249(2) BGB, under which a creditor may demand the amount needed when a thing is damaged, and applied it also to a collective item such as a lock system. For you this means that a claim for a thousand euros is not automatically justified as long as nothing has been replaced and replacement is not necessary.
| Case | What the landlord may claim | What matters |
|---|---|---|
| Single key lost, simple lock | Replacement key or cylinder replacement | Loss and fault, actual costs |
| Key of a lock system lost | Possibly costs of replacing the system | Risk of misuse, necessity, actual replacement |
| Replacement only announced | No compensable loss yet | BGH 2014: loss only with actual replacement |
| Move-out with incomplete key return | Possible claims depending on the case | Handover protocol, number of keys |
When is replacing the lock system really necessary?
The BGH ties it to the risk of misuse. That means the landlord may not simply renew any system at your expense. What counts is whether there is a real possibility that unauthorised persons use the lost key. The following examples are our own illustrations and not statements of the BGH. A key lost in your own household that soon turns up is judged differently from a key presumably lost in the street that could be linked to an address. The individual case decides. Therefore ask for the need for replacement to be justified and for a cost estimate, rather than accepting lump sums.
Prevention takes little effort: do not attach an address to your key ring, keep spare keys safe and hand keys to visitors or tradespeople only against handover and return. Whoever loses a key to a lock system should also think straight away about whether third parties could link it to a flat. That assessment belongs in your message to the landlord, because it is central to the question of misuse risk.
Does personal liability insurance help with a lost key?
That depends on the contract. According to Stiftung Warentest, it varies whether private liability insurance covers the loss of private keys. Some tariffs include the loss of third-party keys, others only as an add-on with a limited sum, others not at all. Check the insurance terms before a loss and ask whether keys of rented flats and lock systems are covered. On liability cover during studies, see liability insurance in a shared flat and your own flat (in German) and co-insurance through your parents (in German). If you are unsure, a personal consultation with Academycon can help, see how we work (in German).
What applies to keys and copies in a shared flat?
According to Stiftung Warentest, tenants may not copy keys without the landlord’s knowledge. You may have additional keys made at your own expense if the number handed over is not enough, provided the landlord agrees. In a shared flat, the contract partner, meaning the main tenant, is in principle liable to the landlord. How this is divided among main tenants, subtenants or flatmates depends on your contracts, see main tenant or subtenant (in German). Agree internally that a flatmate who loses a key also bears the follow-up costs.
What to do after losing a key, step by step
- Search thoroughly before reporting the loss and think about where the key was last.
- Inform the landlord immediately in text form and describe which key is missing.
- Ask whether a replacement is necessary and request reasons and a cost estimate.
- Report the case to your liability insurer if keys could be insured.
- At move-out, record the number of keys in the handover protocol (in German).
Frequently asked questions
Do I have to have the lock replaced immediately after losing a key?
No. What matters is whether replacement is necessary. If the landlord decides to replace, under BGH case law it can claim compensable loss only once the replacement has actually taken place.
Can the landlord keep the deposit?
For a provable loss, the landlord can rely on the deposit in the final settlement. You do not have to accept loss and amount if they are not substantiated. On settlement see getting your deposit back (in German).
Does liability insurance pay for students too?
That depends on the tariff and the key cover. Check the terms and ask the insurer whether third-party keys and lock systems are covered.
What if I find the key after the replacement?
Tell the landlord in writing immediately. If the replacement has not yet happened, the basis for a replacement at your expense falls away under the BGH logic, because without a risk of misuse it is not necessary. If it has happened, the individual case determines whether and what costs remain.
What to do next
- Look for the key and report the loss to the landlord in text form.
- Have the necessity and the costs of any replacement substantiated.
- Check your liability insurance and report the loss there.
- At move-out, record the number of keys in the handover protocol.
Related guides
- Housing during your studies: overview (in German)
- Liability insurance in a shared flat and your own flat (in German)
- Handover protocol when moving out (in German)
- Getting your deposit back after moving out (in German)
Sources: Federal Court of Justice: press release no. 42/2014, judgment VIII ZR 205/13 of 5 March 2014 | Stiftung Warentest: flat keys and tenant rights (only the freely accessible introduction was evaluated)
Last updated: November 2026. This guide is general information, not individual advice.
