Can also make a Raspberry Pi act as a transmitter (https://github.com/F5OEO/rpitx), which could hit the zwave frequency but not the zigbee one. (Also, make sure to put a low pass filter on it.)
https://github.com/F5OEO/rpitx
And it does work with nearly every RPi.
And unlike only doing FM (97MHz-108MHz), it can emit from an IQ datastream from 10KHz to 1.5GHz.
https://osmocom.org/projects/osmo-fl2k/wiki (repurposing a USB-VGA dongle as analog source)
https://github.com/F5OEO/rpitx (repurposing bitbang/PWM GPIO; we had weird problems with data corruption when we were trying to use it as a radio modem, but maybe you will have more luck)
https://bellard.org/dvbt/ (repurposing standard VGA card, but it's probably not worth it since fl2k is way better)
(beware that low quality of the transmitter usually means it will cause interference with other stuff. However, all of these have such a low power that if you will not use an amplifier, it will be OK, the interference will be probably undetectable outside of the room where the transmitter is)
It started with piFM [1] where the possibility was explored to modulate the internal PLL Raspberry Pi with FM and output it on pin GPIO4. This was then further refined and a PWM phase and amplitude modulation technique was applied which made it possible to generate SSB signals [2]. Based on this rpitx [3] was then created which made it possible to basically modulate any type of signal, enabling to use a raspberry pi for analog and digital broadcasts, and to replace key fobs for RF smart plugs and other wireless devices. So yes, it is possible..
[1] GPIO4 piFM transmitter, by Oliver Mattos and Oskar Weigl http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...
[2] Direct SSB generation by frequency modulating a PLL, by Guido http://pe1nnz.nl.eu.org/2013/05/direct-ssb-generation-on-pll...
[3] Universal I/Q TX for rpi, Evariste Courjaud, https://github.com/F5OEO/rpitx
I attached a low-pass filter to the GPIO pin and was able to control my ceiling fan with my Raspberry Pi.
[0] https://github.com/F5OEO/rpitx
Edit: This generates square waves which have harmonics. You will transmit signals on unintended frequencies if you don't use a filter.
https://hackaday.com/2019/06/05/mobile-sigint-hacking-on-a-c...
If it wasn't for F5OEO's Rpitx library, I would have been stuck with non-SDR Tx. https://github.com/F5OEO/rpitx
Same is possible with Raspberry Pi GPIO:
I have a „Hörmann“ garage door opener. For a long time, I want to use my phone instead of the original sender. Therefore, I thought to run a raspberry and send the signal from there.
I recorded the signal with HackRF One as .wav, the problem here is that HackRF records with a sampling rate much higher than 48kHz (by default it is 10MHz!). So one has to downsample the recorded file, which I did with Matlab (downsample(signal, „fs_of_record/fs_for_rpitx“)). The resulting .wav signal is now send at 433MHz (either my garage door listens their too, or 2nd harmonic works?!)