Sentinel : Is it free to use?

I have a very simple question. Does defender Sentinel comes with a price? Or is it free to use forever? I don't see any payments related info anywhere. So I believe it's free to use forever.
If it's not then please consider providing with the details about payment and the limitations in free version.

Defender Sentinel is free to use! There is no end date defined for the free tier at this time, however the OpenZeppelin Defender pricing model is subject to change, as set out in the terms of use at We will provide advance notice if such a change were to take place.

In the free tier, users are limited to 20 Sentinels and 500 Sentinel watch TXs per hour

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Hey Emnul, Thanks for replying.

Can you please rephrase the "500 Sentinel watch TXs per hour" . I didn't get it.

@Solidity_Learner Your Sentinel is limited to watching only 500 transactions per hour. Say you want to watch all transactions that call the Transfer function in your contract. If you have more than 500 calls to the Transfer function in one hour then your Sentinel will be throttled until the next hour.