Delta Sleep

Privacy Policy

Delta Sleep by GSDSi

Effective date: 15 September 2026

Delta Sleep is a free sleep-cycle tracker for iPhone. With your permission, the app can share information about your sleep with GSDSi. We use it to improve how the app estimates sleep, and we may sell or license it, in a form that does not identify you, to researchers and companies for sleep research and for improving sleep tracking and sleep management. That is what keeps the app free. It is never used for advertising or marketing. Every kind of sharing described here is optional and off until you turn it on. This policy explains exactly what we may collect, what we do with it, who we may sell it to, what we will never do, and how you stay in control.

The short version

• The app is free because we may sell or license the data you choose to share, after removing anything that identifies you, for sleep research and for improving sleep tracking and management. We tell you this before you share anything, and you can say no.
• We never collect your name, email, or anything that identifies you, and we never share audio.
• We do not use your data for advertising, and the app contains no ads or ad trackers.
• Everything we collect is opt-in. The app works fully with all sharing off, and each choice can be changed at any time. A separate "Do not sell my data" switch lets you share with us for improving the app but keep your data out of any sale.
• Sharing sleep summaries includes your approximate, city-level location unless you turn location off in the app's settings or decline the iOS location prompt. Raw motion data is a separate choice.
• You can delete everything we hold about you from inside the app.

What the app records on your phone

Motion data. While you record a night, Delta Sleep reads your iPhone's accelerometer to measure how much you move. The app keeps two movement measurements for each 30-second period: how much the phone moved, and how still it was. The raw readings from your most recent night are kept on your phone until the next night replaces them, so a night can be re-analysed if the app's sleep detection improves. They are not uploaded unless you have chosen to share raw motion data (see below).

Sleep sessions. For each night, the app stores the start time, end time, and an estimated sleep stage (awake, light, deep, or REM) for each 30-second period. From these it computes the figures you see, such as total sleep, efficiency, and time per stage.

Sound level, if you allow the microphone. To keep tracking while your screen is locked, the app listens through the microphone overnight. It measures only how loud the room is, twice a second, to detect movement and snoring. Audio is analysed on your phone in the moment and is never recorded, saved, or uploaded. What the app keeps is a single loudness number for each 30-second period. If you don't allow the microphone, the app still works: the screen stays on during tracking, or rain sounds play all night instead.

Settings. Your wake-up alarm time, rain-sound preference, timer duration, sleep goal, and whether the bedtime reminder is on. From your recorded nights and your sleep goal the app also works out a weekly average and sleep-debt figure, on your phone.

Battery status. The app checks whether your phone is charging so it can remind you to plug in before a night of tracking. This is read in the moment and is never stored or shared.

Lock Screen Live Activity. While a night is being recorded, the app can show its progress on your Lock Screen and in the Dynamic Island: the time tracking started, the current estimated stage, your alarm time, and whether the microphone is in use. This is drawn by iOS from data on your phone and involves no server.

All of this stays on your phone unless you choose to share it with us.

What we collect, if you say yes

None of this is required. Sleep summaries are the main choice; approximate location comes with them unless you turn it off; raw motion data is a separate switch.

1. Sleep summaries. After each recorded night, the app sends the start and end time, the sequence of 30-second stage estimates, the two movement measurements for each 30-second period (how much the phone moved and how still it was, not the raw readings), the loudness number for each 30-second period if you allowed the microphone (never any audio), which features were on (alarm, rain sounds, smart wake) and their durations, plus the app version, iOS version, and iPhone model. These are tied to a random install identifier generated on your phone. On its own, this identifier does not tell us who you are.

2. Your approximate location. When sharing is on, the app also records your approximate location (city-level, as provided by iOS's reduced-accuracy option) and time zone at the start of each recorded night. This is included by default; you can turn it off with the "Share approximate location" switch in the app's settings or by declining the iOS location prompt, and summaries are still shared without it. We use it to understand how sleep varies by region, season, and time zone. We never ask for precise location and we never track your location in the background or while the app is not recording.

3. Raw motion data. If you allow it, the app uploads the accelerometer readings from your recorded nights alongside the sleep summary. Raw motion data is the most valuable input for improving how the app tells sleep stages apart. It is a record of how much your phone moved on the mattress; it cannot be used to hear, see, or locate you.

If you email us, we receive your email address for that correspondence only.

We do not collect your name, email address, phone number, contacts, photos, audio, browsing history, or any advertising identifier. The app has no accounts and no sign-in.

Why we collect it

• To improve sleep detection. The app estimates sleep stages from movement. Real nights from real users, and especially raw motion data, let us tune and validate those estimates.
• To improve the app. Understanding which features are used, how long nights last, and how sleep differs by region helps us decide what to build and fix.
• To fix problems. Technical details help us reproduce bugs specific to a device or iOS version.

We do not use your data to build a profile of you for any other purpose, to make automated decisions that affect you, or for anything unrelated to Delta Sleep.

How we fund the app: licensing de-identified data for research

Delta Sleep has no price and no ads. Instead, we may sell or license the data you choose to share to researchers and companies, for two purposes only: sleep research, and improving how sleep is tracked and managed. Examples are universities and sleep-science labs, organisations studying population sleep patterns, and companies improving the sleep-tracking or sleep-support features of their products. Every licence restricts use to those purposes and forbids using the data for advertising, marketing, or profiling.

What we sell is de-identified. We never collect your name or email in the first place, and before any data leaves GSDSi for a buyer we also remove the install identifier and round location to no finer than city level. Buyers receive sleep summaries, movement and loudness measurements, approximate location and time zone if you shared them, device model, and app settings, with no way to link them back to you. Every buyer agrees in writing to use the data only for sleep research or improving sleep tracking and management, never for advertising or marketing, not to resell it, not to attempt to re-identify anyone, and not to combine it with other sources to do so.

You control this in two places:

• Don't share at all. Leave sharing off and nothing is collected or sold.
• Share but don't sell. Turn on "Do not sell my data" in the app's settings. We then use your data only to improve Delta Sleep and exclude it from every sale, including sales that happen after you turn the switch on.

What we will never do

• We will never collect your name or email, and we will never sell or share your install identifier or any data in a form that could identify you.
• We will never sell or share audio. None is ever recorded.
• We will never share your data with advertisers, ad networks, or data brokers, license it for advertising or marketing, or use it for targeted advertising.
• We will never combine it with data from other sources to learn more about you than you chose to share.
• We will never request precise location or track you when the app is not recording a night.

Who can see it

Data linked to an install identifier is seen only by GSDSi staff working on the app. We use a cloud hosting provider to store it; that provider processes it on our behalf under contract and has no right to use it for its own purposes. Buyers of de-identified data are described in the section above. We may disclose data if required by law, and we may publish aggregate statistics that cannot identify any individual (for example, average deep-sleep time in a region).

Your choices and rights

• Turning sharing on or off. The app asks about sleep summaries when you first open it, and tells you then that shared data may be sold in de-identified form and that approximate location is included. Location has its own switch in the app's settings, on by default; raw motion data has its own switch, off until you turn it on. Turning any of them off stops that kind of upload immediately and does not change how the app works.
• Do not sell my data. A switch in the app's settings. When on, your data is used only to improve Delta Sleep and is excluded from any sale. This is also how to exercise a "do not sell or share" right where the law provides one.
• Location permission. Location sharing also requires iOS location permission, which you can revoke at any time in Settings > Privacy & Security > Location Services.
• Deleting your data. Choose "Delete my shared data" in the app's settings. We delete all data linked to your install identifier from our systems within 30 days. Deleting the app removes everything stored on your phone.
• Access and portability. Email us and we will send you the data we hold about you. We will ask you for your install identifier, which is shown in the app's settings, because we have no other way to find your data.
• Regional rights. If you live in the European Economic Area, the United Kingdom, California, or another region with data-protection law, you may have additional rights, including to correct your data, to object to processing, and to lodge a complaint with a supervisory authority. Our legal basis for processing under the GDPR is your consent, which you can withdraw at any time.

Storage, security, and retention

Data is sent to our servers over an encrypted connection and stored encrypted at rest. We keep shared data for as long as it is useful for improving the app, or until you delete it. Technical logs that could contain your identifiers are kept for no more than 90 days.

If you use iCloud Backup or back up your phone to a computer, the app's local data is included in that backup like any other app's data. Those backups are governed by Apple's privacy policy.

Permissions the app may ask for

Notifications. The app asks permission to show local notifications for four things: a backup wake-up alert at your alarm time if you use the gentle alarm; a reminder to plug in your phone if a night starts while it isn't charging; a bedtime reminder 30 minutes before the bedtime worked out from your alarm and sleep goal, which you can turn off in the app's settings; and a summary on Sunday mornings of your average sleep and sleep debt for the week. Every notification is created on your device from data on your device and never involves a server.

Location. Asked the first time you start a night with sharing on. The app requests approximate location while in use, never precise location and never in the background. Declining keeps location out of your shared data.

Microphone. Asked the first time you start a night. Used to measure room loudness while you sleep so tracking continues with the screen locked; nothing is recorded. You can decline or revoke it any time in iOS Settings, and the app will keep the screen on or play rain all night instead.

Apple Health. Off unless you turn on "Save nights to Apple Health" in Settings. Then each night's sleep stages are written to the Health app on your phone, which asks your permission first. Delta Sleep never reads anything from Health, and nothing in Health is ever sent to us or to anyone else. Turning the setting off stops new nights being written; deleting a night in the app removes it from Health.

Motion. Reading the accelerometer does not require a permission prompt on iOS. The app does not use the Motion & Fitness features that track steps or activity.

Children

Delta Sleep is not directed at children under 13, and we do not knowingly collect data from them. If you believe a child has shared data with us, contact us and we will delete it.

Not medical advice

Delta Sleep estimates sleep stages from movement alone. It is not a medical device and its output should not be used to diagnose or treat any condition. Consult a healthcare professional for concerns about your sleep.

Changes to this policy

If we change what we collect, how we use it, or whether and how we sell it, we will update this policy, change the effective date, and ask for your consent again inside the app before the new practices take effect. Earlier versions of this policy stated that data would never be sold; that changed on 15 September 2026, and anyone who shared under the earlier wording is asked again before any of their data is included in a sale.

Contact

Questions and requests about your data can be sent to jensen@gsdsi.com.