I was looking into getting myself a camera pen or what many know as a "spy pen" since the beginning of February. There was three things I was looking for in a camera pen, a discrete camera, a SD card slot & actual pen functionality. Some bonus features would be a battery lasting at least an hour, a mic & changeable pen tips although you can just fill it up with a syringe. Finding a camera pen discrete enough might be hard since many devices have indicator lights & needs a place for a small camera sensor to be.
I came across this pen camera on amazon, the brand is sirgawain & they sell more than just pen cameras. This pen camera was advertised on amazon as a full HD 1080p camera with about 70 minutes of battery, 10 minutes longer than the 1 hour I was looking for. It has one button control, meaning recording, taking photos & toggling the power is all done with one button. The camera is located under the clip along with a mic somewhere at the bottom.
The camera pen has an micro SD card slot, supporting up to 128GB. This pen camera also has a micro USB port for charging & data transfer, making it easy to charge it while sorting through videos & photos. Be sure to format the SD card on your computer before you insert it into the pen camera, otherwise it may not save you videos & photos. If you want to save space on the pen camera, click the button 3 times to enable motion detection mode. I haven't tried it since I've got cameras.
As far as being discrete, I'd say use it in a pen holder or somewhere where light won't shine on the clip bringing attention to the lens, maybe in a breast pocket with other pens around it so all the attention isn't drawn onto it or where you can play dumb. I will be testing it further & will do an update blog post. I made a YouTube video showing what to expect in 3 different scenarios. I also taken photos in those three scenarios with more to come in the future, you'll be able to find them in my hidden camera gallery.