# Health Data Server vs Understanding Sleep

The clearest difference is price: Understanding Sleep at Free against Health Data Server's $4.99. Understanding Sleep also leads on in-app purchases (none vs 6). Health Data Server's advantage is device support (4 vs 2) and iOS requirement (14.0 vs 16.0). On update cadence and ads there is nothing between them.

Understanding Sleep is free to download; Health Data Server costs $4.99 up front. Health Data Server sells 6 in-app purchases, starting at $2.99 per month. Understanding Sleep asks for nothing beyond the download.

Health Data Server ships an update weekly, Understanding Sleep fortnightly. The most recent releases landed on September 24, 2026 and September 10, 2026 respectively.

## The numbers

| Metric | Health Data Server | Understanding Sleep |
| --- | --- | --- |
| Price | $4.99 | **Free** |
| Rating | **[3.9 (41 ratings)](https://appshunter.io/ios/app/health-data-server/id1496042074/reviews)** | — |
| Number of ratings | **41** | — |
| Positive reviews | 81.8% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Weekly** | Fortnightly |
| Monetization | Free with in-app purchases | — |
| Size | 27 MB | 91 MB |
| Requires iOS | **14.0** | 16.0 |
| Devices | **iPhone, iPod, Mac, Apple Watch** | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [Aaron DeLory](https://appshunter.io/developer/1496042073) | [Avicenna Research Inc.](https://appshunter.io/developer/1137173051) |

## What reviewers say

### Health Data Server

[App page](https://appshunter.io/ios/app/health-data-server/id1496042074)

Stream real-time health data from your Apple Watch to your overlay. Display heart rate, calories, and more with customizable animations and sounds. Save workout data to Apple Health.

**Highlights:** Stream heart rate from Apple Watch, Display calories burned, Customizable overlay appearance, Heartbeat animation and sound, Save workout data to Apple Health, Access extensive HealthKit data

**Features:** Family Sharing, Apple Watch app, Vision Pro support

**In-app purchases (6)**

| Purchase | Price | Billing |
| --- | --- | --- |
| HDS Cloud Monthly | $2.99 | per month |
| HDS Cloud Yearly | $29.99 | per year |
| Small Tip | $0.99 | one-time |
| Medium Tip | $2.99 | one-time |
| Large Tip | $4.99 | one-time |
| Make Up the Difference | $49.99 | one-time |


### Understanding Sleep

[App page](https://appshunter.io/ios/app/understanding-sleep/id6763775915)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


## Frequently asked questions

### Is Health Data Server free?

Health Data Server costs $4.99, and also offers in-app purchases.

### Is Understanding Sleep free?

Understanding Sleep is free to download, with no in-app purchases.

### Do Health Data Server or Understanding Sleep have ads?

Neither Health Data Server nor Understanding Sleep shows ads.

### Which is updated more often, Health Data Server or Understanding Sleep?

Health Data Server ships an update weekly, and Understanding Sleep fortnightly. Most recently, Health Data Server was updated on September 24, 2026 and Understanding Sleep on September 10, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*