Check here in the Hikvision download portal for Hikvision's HiWatch products:
DOWNLOAD PORTAL
Click on the ReadMe at the bottom of the list.
Look for your HiWatch product in that text document:
(the current list on 23rd October 2018 is reproduced here)
G0:
1 HWI-B140H(2.8mm)(HiWatch标配)
2 HWI-B140H-M(2.8mm)(HiWatch标配)
3 HWI-B140H(4mm)(HiWatch标配)
4 HWI-B140H-M(4mm)(HiWatch标配)
5 HWI-D140H(2.8mm)(HiWatch标配)
6 HWI-D140H-M(2.8mm)(HiWatch标配)
7 HWI-D140H(4mm)(HiWatch标配)
8 HWI-D140H-M(4mm)(HiWatch标配)
9 HWI-T240H(2.8mm)(HiWatch标配)
10 HWI-T240H(4mm)(HiWatch标配)
11 HWI-B640H-Z(2.8-12mm)(HiWatch标配)
12 HWI-B640H-V(2.8-12mm)(HiWatch标配)
13 HWI-D640H-Z(2.8-12mm)(HiWatch标配)
14 HWI-D640H-V(2.8-12mm)(HiWatch标配)
E3
1 HWI-B120H(2.8mm)(HiWatch标配)
2 HWI-B120H-M(2.8mm)(HiWatch标配)
3 HWI-B120H(4mm)(HiWatch标配)
4 HWI-B120H-M(4mm)(HiWatch标配)
5 HWI-D120H(2.8mm)(HiWatch标配)
6 HWI-D120H-M(2.8mm)(HiWatch标配)
7 HWI-D120H(4mm)(HiWatch标配)
8 HWI-D120H-M(4mm)(HiWatch标配)
9 HWI-T220H(2.8mm)(HiWatch标配)
10 HWI-T220H(4mm)(HiWatch标配)
11 HWI-B620H-Z(2.8-12mm)(HiWatch标配)
12 HWI-B620H-V(2.8-12mm)(HiWatch标配)
13 HWI-D620H-Z(2.8-12mm)(HiWatch标配)
14 HWI-D620H-V(2.8-12mm)(HiWatch标配)
E4:
1 HWI-B120(2.8mm)(HiWatch标配)
2 HWI-B120-M(2.8mm)(HiWatch标配)
3 HWI-B120(4mm)(HiWatch标配)
4 HWI-B120-M(4mm)(HiWatch标配)
5 HWI-D120(2.8mm)(HiWatch标配)
6 HWI-D120-M(2.8mm)(HiWatch标配)
7 HWI-D120(4mm)(HiWatch标配)
8 HWI-T220(2.8mm)(HiWatch标配)
9 HWI-T220(4mm)(HiWatch标配)
10 HWI-D120-M(4mm)(HiWatch标配)
E2:
BASELINE ALREAD SUPPORT
1 HWI-B100(2.8mm)(HiWatch标配)
2 HWI-B100-M(2.8mm)(HiWatch标配)
3 HWI-B100(4mm)(HiWatch标配)
4 HWI-B100-M(4mm)(HiWatch标配)
5 HWI-D100(2.8mm)(HiWatch标配)
6 HWI-D100-M(2.8mm)(HiWatch标配)
7 HWI-D100(4mm)(HiWatch标配)
8 HWI-D100-M(4mm)(HiWatch标配)
9 HWI-T200(2.8mm)(HiWatch标配)
10 HWI-T200(4mm)(HiWatch标配)
E2C1:
HWC-C100-D/W
It shows that your HiWatch IPC-D120 IP camera uses the E4 firmware.
At that same
Hikvision portal page click on the link titled E4.
You will see that currently it lists and offers only one firmware version (V5.5.4) for your camera.