I bought a sleep tracker from Aliexpress, which can calculate respiratory rate in real time:

https://www.aliexpress.com/item/4000016737162.html?spm=a2g0s.9042311.0.0.27424c4d8PccMO

Unfortunately, the Happy Sleep app said, that I was sleeping, when I was practicing breath meditation. Therefore, I was looking for a sleep tracker which is based on EEG data.

I found the SpiSOP sleep lab, which is OpenBCI based:

OpenBCI

On Aliexpress, affordable OpenBCI compatible EEG modules can be found:

https://de.aliexpress.com/item/4000244594585.html?spm=a2g0s.9042311.0.0.27424c4d9gZnYN

OpenBCI wifi module:

https://de.aliexpress.com/item/4000244557551.html?spm=a2g0o.productlist.0.0.64576eeac9Fb9q&algo_pvid=1b55566e-a9fa-4b94-9c9a-244927dfe5f8&algo_expid=1b55566e-a9fa-4b94-9c9a-244927dfe5f8-11&btsid=0b0a556516174129187305953e52b8&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

TENOCOM 20 Channels EEG Head CAP:

https://de.aliexpress.com/item/4000783697430.html?spm=a2g0o.store_pc_topSellerIng.8148356.1.4a832503WRqPpV

Disposable EEG Caps For Polysomnograph

https://m.tenocom.com/shuimian/spzdj/7479.html

Alternative software:

Sleep: An Open-Source Python Software for Visualization, Analysis, and Staging of Sleep Data:

https://www.frontiersin.org/articles/10.3389/fninf.2017.00060/ful

4.3.22

Alternative EEG cap Adult Sleep EEG cap (Greentek Sensors):