These Terms of Service (Terms) govern your use of the kaldr mobile application, kaldr.app, and related services (together, the Services).
The Services are provided by Crystalab LLP, a limited liability partnership registered in England and Wales under company number OC446298, with its registered office at 71–75 Shelton Street, London, WC2H 9JQ, United Kingdom (Crystalab, we, us, or our).
These Terms are effective from July 13, 2026.
By creating an account, downloading or using the app, or otherwise using the Services, you agree to these Terms. If you do not agree, do not use the Services.
1. Eligibility
You must be at least 18 years old to use kaldr. By using the Services, you confirm that you are 18 or over and legally able to enter into these Terms.
The Services are intended for individual consumers. They are not intended for clinical, emergency, professional medical, or supervised patient use.
2. Important health and safety warning
Breathing exercises, breath-holding, and cold exposure carry real risks, including dizziness, fainting, falls, cold shock, loss of consciousness, seizure, heart or circulatory stress, hypothermia, injury, and death. Read this section before beginning.
Breathing practice
- Always practise seated or lying down in a safe place where falling or losing consciousness cannot cause injury.
- Never perform breathing exercises or breath holds while standing, walking, driving, cycling, operating machinery, or performing any activity that requires continuous attention.
- Never perform breathing exercises or breath holds in or near water, including in a bath, shower, pool, hot tub, open water, or sauna. Do not combine the breathing practice with the cold-shower practice.
- Do not compete with yourself or others. End a breath hold whenever you need to breathe.
- Stop immediately if you experience chest pain, severe shortness of breath, confusion, visual disturbance, numbness, panic, loss of coordination, or unusual or persistent discomfort.
Cold exposure
- Cold water can cause an involuntary gasp, rapid breathing, loss of coordination, changes in blood pressure, and stress on the heart and circulation.
- Begin gradually, ensure the shower area is not slippery, and make sure you can leave or warm yourself safely.
- Never lock yourself in, use restraints, or continue because a timer tells you to. Stop immediately if you feel faint, confused, numb, weak, unwell, or unable to control your breathing.
- Do not use the cold-exposure feature in open water or in circumstances where fainting or loss of coordination could cause drowning or prevent escape.
Medical considerations
Consult a qualified medical professional before using kaldr if you are pregnant, take medication that affects your heart or blood pressure, or have any medical concern. Do not use the practices without medical clearance if you have, or may have:
- A heart, cardiovascular, circulatory, or respiratory condition
- High or low blood pressure
- Epilepsy, seizures, or a history of fainting or loss of consciousness
- Raynaud's phenomenon, cold urticaria, impaired temperature sensation, or another condition affected by cold
- A recent injury or operation, or another condition that could make breathing exercises or cold exposure unsafe
This list is not exhaustive. Advice from a clinician who knows your medical history takes priority over anything shown in kaldr.
kaldr is a general wellness and fitness tool. It does not provide medical advice, diagnosis, monitoring, treatment, prevention, or emergency services, and it is not a medical device or substitute for professional care. If you believe you have a medical emergency, stop and contact local emergency services.
You are responsible for choosing whether, where, and how to perform a practice and for stopping when necessary. No timer, cue, streak, statistic, or suggested duration is a target you must reach.
3. Your account
You must provide accurate account information and keep your sign-in credentials secure. You are responsible for activity carried out through your account unless it results from our failure to use reasonable care.
Tell us promptly at support@kaldr.app if you believe your account has been compromised. You may not sell, transfer, or make your account available to another person.
Your practice history is private to your account and is not a public profile. Our handling of account and practice information is described in the Privacy Policy.
4. Licence to use kaldr
Subject to these Terms, Crystalab gives you a limited, personal, non-exclusive, non-transferable, non-sublicensable, and revocable licence to install and use the app for your own non-commercial wellness and fitness practice.
If you download kaldr from Apple's App Store, Apple's standard end-user licence agreement also applies to the app licence. These Terms supplement that agreement for kaldr accounts and Services. Your use of an app store is also subject to the store's applicable terms.
5. Free and paid features
kaldr is currently offered without a subscription. We may introduce paid features, subscriptions, or trials in the future.
Before any purchase, we will show the applicable price, billing period, included features, trial terms, automatic-renewal terms, and cancellation method. Mobile purchases will normally be billed and managed by Apple or Google, not directly by Crystalab. The relevant store's payment and refund rules apply, subject to your mandatory consumer rights.
We will not enrol you in a paid subscription merely because you use the current free service. Any paid plan will require a separate purchase confirmation.
6. Advertising and third-party services
The Services may display advertising supplied by Google AdMob and its advertising partners. Ads may be personalised only where permitted by your consent, device settings, and applicable law. Limited, contextual, or non-personalised ads may still be displayed when personalisation is unavailable or refused.
Third-party advertisements and links are provided by their respective advertisers. Crystalab does not endorse an advertised product merely because an ad appears in kaldr and is not responsible for a third party's content, availability, products, or transactions. Use appropriate care before relying on wellness or health claims made by an advertiser.
The Services also rely on providers including Google Firebase, Apple, PostHog, Sentry, and Vercel. Their services may be subject to their own terms and privacy policies.
7. Acceptable use
You must not misuse the Services. In particular, you must not:
- Use the Services unlawfully or in a way that harms, threatens, or infringes the rights of another person
- Access or attempt to access another user's account or information
- Probe, bypass, disable, or interfere with authentication, security, rate-limiting, or technical protections
- Introduce malware, scrape the Services, or use bots, scripts, or automation without our written permission
- Fabricate or flood sessions, requests, ad interactions, or other events in a way that creates unreasonable load or corrupts statistics
- Create or use multiple accounts to evade rate limits, restrictions, suspensions, trials, charges, or enforcement
- Manipulate advertisements, impressions, clicks, attribution, payments, or promotions
- Reverse-engineer the Services except where applicable law expressly permits it despite this restriction
- Resell, sublicense, copy, or commercially exploit the Services or their content without written permission
- Use kaldr to provide medical care, supervise patients, or make clinical or emergency decisions
Unusually high session or request volumes, including implausible repeated activity, may be treated as an abuse signal and investigated. A signal is not necessarily proof of a breach.
8. Suspension and termination
We may restrict or suspend an account where we reasonably believe this is necessary to investigate abuse, protect users or systems, prevent fraud, comply with law, or address a breach of these Terms.
For a minor or remediable issue, we will normally provide notice and a reasonable opportunity to correct it. We may act immediately where there is a material breach, fraud, unlawful activity, a security threat, risk of harm, or unreasonable technical load. Where practicable, a person will review relevant information before a non-urgent permanent termination.
We may terminate an account after notice if a breach is not corrected, or without prior notice for a serious breach or urgent risk. If we terminate a future paid service and you are not at fault, we will provide any refund required by law or the applicable app store's rules.
You may stop using kaldr at any time. You can permanently delete your account and practice history through Settings → Danger zone → Delete account. See the account deletion instructions.
Sections that by their nature should continue after termination—including intellectual property, liability, dispute, and general provisions—will remain in effect.
9. Intellectual property
Crystalab and its licensors own the Services, including their software, design, text, graphics, audio, branding, and other content, except for rights belonging to third parties. These Terms do not transfer ownership to you.
kaldr and associated branding are identifiers of Crystalab. Other names and trademarks belong to their respective owners. kaldr is not affiliated with, endorsed by, or sponsored by Wim Hof or the Wim Hof Method organisation.
If you voluntarily provide suggestions or feedback, you allow us to use them without restriction or payment, but you retain ownership of any rights you may have in the original feedback.
10. Service operation and changes
We use reasonable care and skill in providing the Services. However, digital services sometimes experience interruption, delay, data-sync failure, device incompatibility, or error. Offline writes may remain pending until a connection is available.
We may update the app, add or remove features, impose reasonable technical limits, or discontinue all or part of the Services for valid reasons such as security, legal compliance, provider changes, technical sustainability, or product development. Where a change materially disadvantages users, we will provide reasonable notice where practicable and honour applicable refund and consumer rights.
You are responsible for maintaining a compatible device, supported operating system, network access when synchronisation is required, and reasonable device security.
11. Consumer rights and disclaimers
Nothing in these Terms excludes rights or remedies that cannot legally be excluded. If you are a UK consumer, this includes your rights under the Consumer Rights Act 2015. Consumers elsewhere may have additional mandatory rights under local law.
Subject to those rights, we do not promise that the Services will always be available, uninterrupted, error-free, or suitable for a medical, clinical, or particular personal objective. Progress estimates, streaks, and statistics are informational and can be affected by device clocks, interrupted sessions, offline synchronisation, and technical errors.
We are not responsible for harm caused by ignoring safety warnings, using the Services contrary to these Terms, continuing after symptoms arise, combining breath-holding with water or another hazardous activity, or relying on kaldr as medical advice. This does not exclude responsibility that the law does not allow us to exclude.
12. Liability
Nothing in these Terms limits or excludes liability for:
- Death or personal injury caused by our negligence
- Fraud or fraudulent misrepresentation
- Breach of mandatory consumer rights
- Any other liability that cannot legally be limited or excluded
If we fail to comply with these Terms, we are responsible for loss or damage that is a foreseeable result of our breach or failure to use reasonable care and skill. We are not responsible for loss or damage that was not reasonably foreseeable when you accepted these Terms.
The Services are supplied for personal and non-commercial use. To the extent permitted by law, we are not responsible for business losses, including lost profit, revenue, business, opportunity, goodwill, or business data.
For liability that can lawfully be limited, Crystalab's total aggregate liability arising from the Services or these Terms will not exceed the greater of £100 or the amount you paid for the Services during the 12 months before the event giving rise to the claim. This cap does not apply to the liabilities listed at the beginning of this section or where applying it would be unfair or unlawful under mandatory consumer law.
13. Privacy
Our Privacy Policy explains what information we collect, how we use it, advertising and analytics choices, international transfers, retention, and account deletion. It is not incorporated as a contractual promise beyond what applicable law requires, but we remain responsible for complying with applicable privacy law.
14. Changes to these Terms
We may update these Terms for valid reasons, including changes to the Services, security, law, providers, or business model. We will update the date at the top.
For a material change, we will provide reasonable advance notice by email or a prominent in-app notice where practicable. Changes will not retroactively take away rights already accrued. If you do not agree to revised Terms, you should stop using the Services and may delete your account before the revised Terms take effect.
15. Governing law and disputes
These Terms are governed by the law of England and Wales. The courts of England and Wales have jurisdiction, but if you are a consumer living elsewhere, you may also bring proceedings in your local courts and rely on mandatory protections of the law of your home country where applicable.
Before beginning formal proceedings, please contact support@kaldr.app and provide a description of the problem. We will try to resolve it informally without restricting either party's right to seek urgent or other lawful relief.
16. General
If a court finds part of these Terms unlawful or unenforceable, the remaining parts will continue to apply. A delay in enforcing a right is not a waiver of that right.
You may not assign your rights under these Terms without our written consent. We may transfer our rights and obligations as part of a reorganisation, merger, sale, or transfer of the Services, provided this does not reduce your mandatory consumer rights.
Except for app-store rights arising under their own terms and licences, these Terms do not give enforcement rights to a person who is not a party to them.
17. Contact
Questions about these Terms or the Services can be sent to:
Crystalab LLP
71–75 Shelton Street
London, WC2H 9JQ
United Kingdom
support@kaldr.app
Privacy questions should be sent to privacy@kaldr.app.